Solid polymer electrolyte, a membrane using thereof, a solution for coating electrode catalyst, a membrane/electrode assembly, and a fuel cell

ABSTRACT

A solid polymer electrolyte is made up of a polymer compound having a hydrocarbon aromatic group in the backbone thereof and including a side chain expressed by FORMULA 1:  
                 
wherein “n” is 1, 2, 3, 4, 5, or 6. The solid polymer electrolyte may be incorporated into a membrane and may be used in a solution for covering an electrode catalyst.

CROSS-REFERENCE TO RELATED FILES

This application is a Continuation application of application Ser. No.10/641,076, filed Aug. 15, 2003, which is a continuation application ofSer. No. 09/811,746 filed on Mar. 20, 2001, now U.S. Pat. No. 6,670,065,issued Dec. 30, 2003. The contents of application Ser. No. 09/811,746,filed on Mar. 20, 2001, are incorporated herein by reference in theirentirety.

BACKGROUND OF THE INVENTION

The present invention relates to a low-cost high-durability and highoxidation-resistant solid polymer electrolyte fit for an electrolytemembrane used for fuel cells, electrolysis of water, electrolysis ofhalogenated hydracid, electrolysis of salt (solution), oxygenconcentrators, humidity sensors, and gas sensors, a solid polymerelectrolyte membrane using thereof, a solution for covering electrodecatalyst, a membrane/electrode assembly, and a fuel cell.

A solid polymer electrolyte is a solid polymer material havingelectrolytic groups such as sulfonic groups in polymer chains and hasfeatures of strongly bonding to specific ions and selectively permeatingcations or anions. The solid polymer electrolyte is formed intoparticles, fibers or thin films and used for electrodialysis, diffusiondialysis, cell diaphragms, and so on.

A reformed gas fuel cell comprising a cathode, an anode, and a protonconducting solid polymer electrolyte membrane sandwiched between theseelectrodes supplies a hydrogen gas obtained by reforming hydrocarbons oflow molecular weights such as methane and methanol as a fuel gas to oneelectrode (fuel electrode) and an oxygen gas or air as an oxidizingagent to the other electrode (air electrode), and obtains electromotiveforces by their reactions. Fuel cells for mobile use includes a pair ofelectrodes at both sides of a proton conducting solid polymerelectrolyte, and obtains an electromotive force by providing a fuel suchas methanol and the like to the one electrode (fuel electrode) of thepair of electrodes and providing an oxidizing agent such as oxygen orair to the other electrode (air electrode). Electrolysis of waterelectrically decomposes water by a solid polymer electrolyte membraneinto hydrogen and oxygen.

Fluorine-related electrolyte membrane such as perfluorocarbon sulfonicmembrane having high proton conducting show very high long-term chemicalstability as a solid polymer electrolyte membrane for fuel cells andwater electrolysis. Typical products of the fluorine-related electrolytemembrane are NAFION (perfluorosulfonic acid polymer, trademark ofDuPont), ACIPLEX (perfluorosulfonic acid polymer, trademark of AsahiChemicals Co., Ltd.) and FLEMION (perfluorosulfonic acid polymer,trademark of Asahi Glass Co., Ltd.)

Electrolysis of a salt solution electrically decomposes a water solutionof sodium chloride by a solid polymer electrolyte membrane into sodiumhydroxide, chlorine, and hydrogen. As the solid polymer electrolytemembrane, in this case, the electrolyte membrane is in contact with achlorine gas and a hot and concentrated water solution of sodiumchloride and must be resistant to them. Therefore hydrocarbon-relatedelectrolyte membranes are not available. In general, perfluorocarbonsulfonic membranes having carboxylic groups partially on its surface toprevent inverse diffusion of ions are used as solid polymer electrolytemembranes which is resistant to chlorine gas and hot and concentratedalkaline water.

Basically, the fluorine-related electrolyte represented by carbonsulfonic membranes has very high chemical stability due to C-F bonds.The fluorine-related electrolyte membranes are used not only as solidpolymer electrolyte membranes for fuel cells, water electrolysis, orsalt electrolysis but also as solid polymer electrolyte membranes forelectrolysis of halogenated hydracid. Due to their high protonconductivity, the fluorine-related electrolyte membranes are also usedfor humidity sensors, gas sensors, oxygen concentrators, and so on.

Contrarily, the fluorine-related electrolyte membranes are hard to bemanufactured and very expensive. So their use is very limited, forexample, to solid polymer electrolyte fuel cells for space and militaryfields and to other particular uses. They are hard to use for solidpolymer electrolyte fuel cells as low-pollution power sources forautomobiles and other public uses.

So various aromatic hydrocarbon electrolyte membranes as inexpensivesolid polymer electrolyte membranes have been disclosed such assulfonated poly-ether ether ketone by Japanese Non-examined PatentPublications No. H06-93114 (1994), sulfonated poly-ether sulfone byJapanese Non-examined Patent Publications No. H09-245818 (1997) andJapanese Non-examined Patent Publications No. H11-116679 (1999),sulfonated acrylonitrile butadiene styrene monomer by JapaneseNon-examined Patent Publications No. H10-503788 (1998), sulfonated polysulfide by Japanese Non-examined Patent Publications No. H11-510198(1999), and sulfonated polyphenylene by Japanese Non-examined PatentPublications No. H11-515040 (1999). The aromatic hydrocarbon electrolytemembranes prepared by sulfonating engineer plastics are easier tomanufacture and have a lower cost than fluorine-related electrolytemembranes represented by NAFION. However, one of the demerits of thearomatic hydrocarbon electrolyte membranes is to be easily deteriorated.This reason is revealed by Japanese Non-examined Patent PublicationsNo.2000-106203. It says the main reason is that the structure ofaromatic hydrocarbon is oxidized and broken by hydrogen peroxide whichgenerates in the catalyst layer on the boundary between the solidpolymer electrolyte membrane, and the air electrode (oxidant electrode).

So various trials have been made to prepare a solid polymer electrolytewhich is as resistant to oxidation as the fluorine-related electrolytemembrane sulfonic type polystyrene graft ethylenetetrafluoroethylene(ETFE) co-polymer having a hydrocarbon-related side chain and a mainchain formed

U.S. Pat. Nos. 4,012,303 and 4,605,685 propose a sulfonicpoly-(trifluorostyrene) graft ETFE polymer electrolyte membrane which isprepared by copolymerizing fluorinecarbide-related vinyl monomer andhydrocarbon related vinyl monomer, grafting α, β, β-trifluorostyrenewith the resulting membrane, and attaching sulfonic groups thereto. Thismembrane uses α, β, β-trifluorostyrene which is partially fluorinatedinstead of styrene because the polystyrene side chain having sulfonicgroups is not chemically stable. However, it is very difficult tosynthesize α, β, β-trifluorostyrene which is material of the sidechains. Further, the material as well as NAFION is too expensive to beused as solid polymer electrolyte membranes for fuel cells. Furthermore,α, β, β-trifluorostyrene has low reactivity of polymerization andconsequently the quantity of α, β, β-trifluorostyrene to be grafted forside chains is very small. The conductivity of the resulting membrane isvery low. It is an object of the present invention to provide an easilymanufactured, high durability solid polymer electrolyte which is durableas the fluorine-related electrolyte or has a substantially high chemicalstability, a solid polymer electrolyte membrane making use thereof, asolution for covering the electrolyte catalyst, a membrane/electrodeassembly, and a fuel cell.

SUMMARY OF THE INVENTION

To dissolve the aforesaid problems, we inventors researched themechanism of deterioration of electrolyte membranes and found that themain cause of the deterioration of the aromatic hydrocarbon electrolytemembranes is not the deterioration by oxidation but rather the directbonding of a sulfonic group to an aromatic ring. This direct bondingallows the sulfonic group to be easily cut out from the aromatic ring inthe presence of a strong acid at a high temperature and as the result,causes reduction of its ionic conductivity. Judging from this result,the high-durability solid polymer electrolyte in accordance with thepresent invention is an aromatic hydrocarbon polymer having a sulfoalkylgroup (FORMULA 1) instead of a sulfonic group in the side chain. Thepresent invention can provide low-cost high durability solid polymerelectrolyte which is as durable as the fluorine-related electrolyte orhas substantially high chemical stability, Further, the ionicconductivity of the electrolyte having the sulfoalkyl groups in the sidechains is greater than the ionic conductivity of the electrolyte havingthe sulfonic groups in the side chains (per weight equivalent to ionexchange group). It is assumed that is related to that the sulfoalkylgroups can move more freely than the sulfonic groups.

Said aromatic hydrocarbon polymer compound is preferably poly-ethersulfone polymer compounds, poly ether ether ketone polymer compounds,polyphenylene sulfide polymer compounds, polyphenylene ether polymercompounds, poly-sulfone polymer compounds, or poly ether ketone polymercompounds.

It is preferable that the polymer electrolyte membrane and the solutionfor covering electrode catalysts contain said polymer electrolyte.

In accordance with the present invention, it is preferable that amembrane/electrode assembly for a solid polymer electrolyte fuel cellcomprises a polymer electrolyte membrane and a gas diffusion electrodeunit comprising a cathode and an anode which are placed on both sides ofsaid polymer electrolyte membrane, wherein said polymer electrolytemembrane is any polymer electrolyte membrane stated above, said gasdiffusion electrodes bind fine catalytic metal particles to the surfacesof a conductive material made of carbon with a binder, and said binderis made of any polymer electrolyte stated above.

In accordance with the present invention, it is preferable that a solidpolymer electrolyte fuel cell comprise a polymer electrolyte membrane,one pair of gas diffusion electrodes comprising a cathode and an anodewhich are placed on both sides of said polymer electrolyte membrane, onepair of gas impermeable separators which are provided to sandwich saidgas diffusion electrodes, and one pair of current collecting memberswhich are placed between said solid polymer and said separator, whereinsaid solid polymer electrolyte membrane is made of any polymerelectrolyte membrane stated above and said polymer electrolyte membraneand said gas diffusion electrodes are made of said membrane/electrodeassembly for a solid polymer electrolyte fuel cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure of a unit cell of a solid polymer electrolytefuel cell.

FIG. 2 shows the result of an endurance test of the unit cell of a solidpolymer electrolyte fuel cell.

FIG. 3 is a picture showing the appearance of a 3KW layer-built cell(stack) integrating the unit cells for a solid polymer electrolyte fuelcell.

FIG. 4 shows a relationship between current density and output voltageof a unit cell of a solid polymer electrolyte fuel cell.

FIG. 5 shows the result of an endurance test of the unit cell of a solidpolymer electrolyte fuel cell.

FIG. 6 shows a relationship between current density and output voltageof a unit cell of a solid polymer electrolyte fuel cell.

FIG. 7 shows the result of an endurance test of the unit cell of a solidpolymer electrolyte fuel cell.

FIG. 8 shows a relationship between current density and output voltageof a unit cell of a solid polymer electrolyte fuel cell.

FIG. 9 shows the result of an endurance test of the unit cell of a solidpolymer electrolyte fuel cell.

FIG. 10 shows a relationship between current density and output voltageof a unit cell of a solid polymer electrolyte fuel cell.

FIG. 11 shows the result of an endurance test of the unit cell of asolid polymer electrolyte fuel cell.

FIG. 12 shows a relationship between current density and output voltageof a unit cell of a solid polymer electrolyte fuel cell.

FIG. 13 shows the result of an endurance test of the unit cell of asolid polymer electrolyte fuel cell.

FIG. 14 shows a relationship between current density and output voltageof a unit cell of a solid polymer electrolyte fuel cell.

FIG. 15 shows the result of an endurance test of the unit cell of asolid polymer electrolyte fuel cell.

FIG. 16 shows a relationship between current density and output voltageof a unit cell of a solid polymer electrolyte fuel cell.

FIG. 17 shows the result of an endurance test of the unit cell of asolid polymer electrolyte fuel cell.

FIG. 18 shows a relationship between current density and output voltageof a unit cell of a solid polymer electrolyte fuel cell.

FIG. 19 shows the result of an endurance test of the unit cell of asolid polymer electrolyte fuel cell.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The sulfoalkyl aromatic hydrocarbon electrolyte in accordance with thepresent invention can be any as far as its side chain containssulfoalkyl groups and its main chain contains aromatic rings.Substantially, the aromatic hydrocarbon electrolyte is an aromatichydrocarbon polymer compound prepared by attaching a sulfoalkyl group(represented by FORMULA 1) to engineering plastics or its polymer alloysuch as poly-ether ether ketone (PEEK) having a structural unit(represented by FORMULA 2) developed by ICI Co., Ltd. (Great Britain) in1977, semi-crystalline poly-allyl ether ketone (PAEK) developed by BASF(Germany), poly-ether ketone (PEK) having a structural unit (representedby FORMULA 3) distributed by Sumitomo Chemicals Co., Ltd. and othercompanies, poly-ketone (PK) distributed by Teijin Amoco EngineeringPlastics Ltd., poly-ether sulfone (PES) having a structural unit(represented by FORMULA 4) distributed by Mitsui Chemicals Co., Ltd. andother companies, poly-sulfone having a structural unit (represented byFORMULA 5) distributed by Teijin Amoco Engineering Plastics Ltd., linearor bridged polyphenylene sulfide (PPS) having a structural unit(represented by FORMULA 6) distributed by Toray, Dainippon Ink andChemicals Inc., Tohpren Co., Ltd., Idemitsu Petrochemical Co., Ltd.,Kureha Chemical Industry Co., Ltd. and other companies, and reformedpolyphenylene ether (PPE) having a structural unit (represented byFORMULA 7) distributed by Asahi Chemical Industry Co., Ltd., Japan GEPlastics, Mitsubishi Engineering Plastics Co., Ltd. and SumitomoChemicals Co., Ltd. Among the above polymer compounds, sulfoalkyl PEEK,PAEK, PEK, PK, PPS, and PES are preferable judging from resistance tooxidation of the main chains.

(wherein “R” is a lower alkyl group such as methyl group or ethyl groupor a phenyl group)

Any sulfoalkylation method can be employed to attach sulfoalkyl groupsto aromatic hydrocarbon polymer or its polymer alloy (FORMULA 1). Forexample, one method uses sultone (FORMULA 8) which is described in J.Amer. Chem. Soc., 76, 5357-5360 (1954) to attach a sulfoalkyl group toan aromatic ring.

(wherein “m” is 1 or 2.)

Another method takes the steps of substituting a hydrogen atom of anaromatic ring by lithium, substituting lithium by a halogenoalkyl groupby dihalogenoalkane, and converting the halogenoalkyl group into asulfoalkyl group. A further method comprises the steps of attaching ahalogenobutyl group to an aromatic ring by a tetramethylenehalogeniumion and substituting the halogen atom by a sulfonic group. See FORMULA9.(wherein “x” is halogen.)

The present invention does not limit a method of sulfoalkylating anaromatic hydrocarbon polymer compound, but a method represented byFORMULA 8 is preferable judging from cost reduction.

The equivalent weight of ion exchange group of the polymer electrolyte(that is, sulfoalkylated polymer) in accordance with the presentinvention is 250 g/mol to 2500 g/mol, preferably 300 g/mol to 1500g/mol, more preferably 350 g/mol to 1000 g/mol. If the equivalent weightof ion exchange group exceeds 2500 g/mol, the output performance willreduce and if it falls below 250 g/mol, the water-resistance of saidpolymer will reduce. These are not preferable.

The equivalent weight of ion exchange group in the present inventionrepresents a molecular weight of said sulfoalkylated polymer persulfoalkyl group. Smaller equivalent weight indicates higher degree ofsulfoalkylation. The equivalent weight of ion exchange group can bemeasured by 1H-NMR spectroscopy, elementary analysis, acid-basetitration or non-aqueous acid-base titration stated in Japan PatentPublication H01-52866 (1989) (using a benzene methanol solution ofpotassium methoxide as the normal solution).

The equivalent weight of ion exchange group of the sulfoalkylatedpolymer can be controlled to be in the range of 250 g/mol to 2500 g/molby selecting a compounding ratio of aromatic hydrocarbon polymer andsulfoalkylating agent, a reaction temperature, a reaction time, achemical structure of the aromatic hydrocarbon polymer.

The polymer electrolyte in accordance with the present invention isusually used in a form of membrane in a fuel cell. Any method can beused to form a sulfoalkylated polymer membrane. Typical forming methodsare a solution casting method which forms a membrane from a polymersolution and a molten pressing or extruding method which forms amembrane from a molten polymer. In details, the solution casting methodcomprises the steps of spreading a polymer solution over a glass plateand removing its solvent. The solvent can be any as far as it dissolvesthe polymer and is easily removed from the polymer. Preferable solventsare non-proton polar solvent such as N, N′- dimethylformamide,N,N-dimethylacetoamide, N-methyl-2-pyrolidone, and dimethylsulfoxide,Alkylene glycol such as ethylene glycol mono-methylether, ethyleneglycol mono-ethylether, propylene glycol mono-methylether, and propyleneglycol mono-ethylether, and halogen solvent.

The thickness of said polymer electrolyte membrane can be any butpreferably 10 μm to 200 μm and more preferably 30 μm to 100 μm. Themembrane is preferably thicker than 10 μm to be strong enough for actualuses and thinner than 200 μm to reduce the resistance of the membrane,that is, to increase the power generation performance. The solutioncasting method can control the thickness of the membrane by selecting aconcentration of the polymer solution or thickness of the polymersolution spread over a substrate. The thickness of a membrane sheet madeby the molten pressing or extruding method can be controlled by rollingat a preset rate.

When the electrolyte in accordance with the present invention ismanufactured, additives such as plasticizer, stabilizer, and partingagent can be added to the electrolyte without departing from the spiritand scope of the invention. The gas diffusion electrodes used for amembrane/electrode assembly in a fuel cell are made of conductivematerials carrying catalyst metal particles on them. The gas diffusionelectrodes can contain water repellent and/or binding agent ifnecessary. It is possible to position, outside the catalyst layer, alayer comprising a conductive material without a catalyst and a waterrepellent and/or binding agent if necessary. Catalytic metals availableto the gas diffusion electrodes can be any as far as they accelerateoxidation reaction of hydrogen and reduction reaction of hydrogen. Suchmetals are platinum, gold, silver, palladium, iridium, rhodium,ruthenium, iron, cobalt, nickel, chromium, tungsten, manganese,vanadium, or their alloys. Among these catalysts, platinum is used inmost cases. Usually, the sizes of catalytic metals are 10 angstroms to300 angstroms. These catalysts are preferably deposited on carriers suchas carbon, reducing the quantity of catalysts to be used and materialcosts. The preferable amount of catalyst to be carried by the carrier is0.01 mg/cm² to 10 mg/cm².

The conductive material can be any as far as it is electron conductivesuch as metals and carbon materials. The preferable carbon materials arecarbon black (such as furnace black, channel black, and acetyleneblack), active carbon, graphite, and so on. These carbon materials areused singly or in combination. For example, fluorocarbon is used as awater repellent. As for a binder, it is preferable to use the solutionfor covering the electrode catalysts in accordance with the presentinvention judging from a point of view of bonding property, but otherresins can be used as the binder. In such a case, a preferable binder isa fluoro resin having a water-repellent property and more particularlyhas excellent heat-resistance and oxidation-resistance. Such resins arepoly-tetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinylethercopolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

Further, an electrolyte membrane and an electrode assembling method fora fuel cell are not limited here and any prior method can be used. Onemethod of manufacturing a membrane/electrode assembly comprises forexample the steps of adding platinum catalyst powder carried by carboninto a polytetrafluoroethylene suspension, spreading the mixture over apiece of carbon paper, heat-treating the paper to form a catalyst layer,spreading an electrolyte solution which is the same as the electrolytemembrane over the catalyst layer, and hot-pressing the electrolytemembrane and the catalyst layer in a body. The other methods are amethod of coating platinum catalyst powder in advance with anelectrolyte solution which is the same as the electrolyte membrane, amethod of applying a catalyst paste onto the electrolyte membrane, amethod of electroless-plating an electrode on the electrolyte membrane,and a method of causing the electrolyte membrane to absorb complex ionsof a platinum group and reducing thereof.

A solid polymer electrolyte fuel cell piles up a plurality of unit cellseach of which consists of a membrane/electrode assembly (comprising anelectrolyte membrane and gas diffusion electrodes) and outer plates (agrooved fuel distributing plate having fuel paths and a grooved oxidantdistributing plate having oxidant paths) which also work as currentcollectors with a cooling plate between the cells. It is preferable tooperate a fuel cell at a higher temperature. This is because theactivity of the electrode catalyst increases and as the resultovervoltages on the electrodes reduce at a high temperature. However, asthe electrolyte membrane cannot work without water, the operatingtemperature of the fuel cell must be such that the water may becontrolled. Therefore, the preferable operating temperature of the fuelcell is between a room temperature and 100° C.

The present invention will be explained in more detail from thefollowing description of embodiments. It is to be expressly understood,however, that the embodiments are for purpose of explanation only andare not intended as a definition of the limits of the invention. Theconditions of measuring respective properties are as follows:

(1) Ion Exchange Group Equivalent Weight

We took an exact weight (“a” gram) of sample sulfoalkylated polymer in aglass container which could be tightly sealed, added an excessivecalcium chloride aqueous solution to the content of the glass container,stirred the content for one night, and titrated hydrogen chloride whichgenerated in the glass container with a 0.1 N standard aqueous solutionof sodium hydroxide (potency: f) by using a phenolphthalein indicator(“b” ml). The Ion exchange group equivalent weight (g/mol) wascalculated by Ion exchange group equivalent weight=(1000×a)/(0.1×b×f).

(2) Evaluation of Output Performance of a Unit Cell of the Fuel Cell.

We set an electrolyte bonded with electrodes in a sample unit cell andmeasured the output performance of the unit cell.

We supplied hydrogen gas and oxygen gas at one atmospheric pressure tothe sample unit cell through a water bubbler (at 23° C.) to humidify thegases. The flow rates of the hydrogen gas and the oxygen gas arerespectively 60 ml/min (for hydrogen) and 40 ml/min (for oxygen). Thetemperature of the cell is 70 ° C. We measured the output performance ofthe cell by the H201B charging/discharging unit (Hokuto Denko Co.,Ltd.).

EMBODIMENT 1 (1) Preparation of Sulfopropyl Polyether Sulfone

We prepared sulfopropyl polyether sulfone by setting up a 500-ml 4-neckround bottom flask with a reflux condenser, a stirrer, a thermometer,and a desiccant tube (containing calcium chloride in it), substitutingthe air inside the flask by nitrogen gas, putting 21.6 g ofpolyethersulfone (PES), 12.2 g (0.1 mol) of propansultone and 50 ml ofdry nitrobenzene in the flask, adding 14.7 g (0.11 mol) of aluminumchloride anhydride to the mixture gradually for 30 minutes whilestirring thereof, refluxing the mixture for 8 hours after addition ofaluminum chloride anhydride is completed, adding 500 ml of iced watercontaining 25 ml of concentrated hydrochloric acid to the reactant tostop the reaction, dripping the reactant solution slowly into 1 liter ofdeionized water, filtering the deionized water to recover theprecipitate (sulfopropyl polyethersulfone), repeating mixing theprecipitate with deionized water and suction-filtering the mixture untilthe filtrate becomes neutral, and vacuum-drying the precipitate at 120°C. for one night. The ion exchange group equivalent weight of theobtained sulfopropyl polyethersulfone is 980 g/mol.

The cost of the sulfopropyl polyethersulfone electrolyte is one fiftiethof the cost of perfluorosulfonic electrolyte which is prepared fromexpensive material in five processes because the sulfopropylpolyethersulfone electrolyte is prepared in a single process frompoly-ether sulfone which is very cheap engineering plastics on-market.

We put 1.0 g of obtained sulfopropyl polyethersulfone and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured the ion exchange group equivalent weight of sulfopropylpolyethersulfone. As the result, we found that the ion exchange groupequivalent weight of sulfopropyl polyethersulfone remains unchanged (980g/mol) and that sulfopropyl polyethersulfone is as stable as theexpensive perfluorosulfonic electrolyte. Contrarily as shown by thecomparative example 1 below, the cheap sulfonated aromatic hydrocarbonelectrolyte is deteriorated under the same temperature and hydrolysiscondition. Its ion exchange group equivalent increases up to 3,000 g/mol(which was initially 960 g/mol) and sulfone groups were dissociated. Inother words, the low-cost sulfopropyl polyethersulfone electrolyteunlike the cheap sulfonated aromatic hydrocarbon electrolyte (seeComparative example 1) shows very good chemical stability as well as theexpensive perfluorosulfonic electrolyte, satisfying both low cost andhigh performance.

(2) Preparation of an Electrolyte Membrane

We prepared an electrolyte membrane by dissolving the product obtainedby the above description (1) into a mixture of 20 parts ofN,N′-dimethylformamide, 80 parts of cyclohexanon, and 25 parts ofmethylethylketone so that the solution may contain 5% by weight of theproduct, spreading this solution over a glass plate by spin-coating,air-drying thereof, and vacuum-drying thereof at 80° C. The obtainedelectrolyte membrane I is 42 μm thick and its ion exchange groupequivalent is 5 S/cm.

We put said obtained electrolyte membrane I and 20 ml of deionized waterin a TEFLON-coated hermetic stainless steel container, kept thecontainer at 120° C. for 2 weeks, cooled the container and then measuredits ion exchange group equivalent weight. As the result, we found thatthe ion exchange group equivalent weight of the obtained electrolytemembrane remains unchanged as well as the expensive perfluorosulfonicelectrolyte. The membrane itself is tough enough. Contrarily as shown bythe comparative example 1-(2), the comparatively cheap sulfonatedaromatic hydrocarbon electrolyte II is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropyl polyethersulfone electrolyte unlike the cheap sulfonatedaromatic hydrocarbon electrolyte (see Comparative example 1-(2)) showsvery good chemical stability as well as the expensive perfluorosulfonicelectrolyte, satisfying both low cost and high performance.

(3) Preparation of a Solution for Covering Electrode Catalyst and aMembrane/Electrode Assembly

We prepared a solution I for covering electrode catalyst by adding asolvent mixture of N,N′-dimethylformamide, cyclohexanon, andmethylethylketone which contains 5% by weight of the product (see (2))to carbon carrying 40% by weight of platinum so that the ratio by weightof platinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly I by coating both sides of the electrolyte membrane I (obtainedby (2)) with said solution I for covering electrode catalyst, and dryingthereof. The obtained membrane/electrode assembly I carries 0.25 mg/cm²of platinum.

Similarly we prepared a membrane/electrode assembly I′ carrying 0.25mg/cm² of platinum by coating both sides of the electrolyte membrane I(obtained by (2)) with said solution II for covering electrode catalyststated by Comparative example 1 (2), and drying thereof.

We prepared a paste (a solution for covering electrode catalyst) byadding an alcohol-water mixture of 5% by weight as perfluorocarbonsulfonic electrolyte to carbon carrying 40% by weight of platinum sothat the ratio by weight of platinum catalyst and the polymerelectrolyte might be 2:1, and dispersing the mixture uniformly. Next wecoated both sides of the electrolyte membrane I (obtained by (2)) withthis paste (solution). However, the paste could not be uniformly spreadover the electrolyte membrane and we could not get a membrane/electrodeassembly. Therefore, the solution I is superior as a solution forcovering electrode catalysts.

We put said obtained membrane/electrode assembly I and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured its ion exchange group equivalent weight. As the result, wefound that the ion exchange group equivalent weight of the obtainedelectrolyte membrane remains unchanged as well as the membrane/electrodeassembly prepared from the expensive perfluorosulfonic membrane and theperfluorosulfonic electrolyte. The membrane itself is tough enough.

Similarly, we put said obtained membrane/electrode assembly I′ and 20 mlof deionized water in a TEFLON-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured its property.

As the result, we found that the membrane/electrode assembly I′ hasenough power generating performance although the electrode was partiallyseparated.

Contrarily as shown by the comparative example 1 (3), themembrane/electrode assembly II prepared by comparatively cheapsulfonated aromatic hydrocarbon electrolyte II and the electrodecatalyst covering solution II is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropyl polychlorofluoroethylene membrane/electrode assembly unlikethe cheap sulfonated aromatic hydrocarbon electrolyte membrane (seeComparative example 1 (3)) is as stable as the expensiveperfluorosulfonic membrane/electrolyte assembly, and satisfies both lowcost and high performance.

(4) Endurance Test of Unit Cells of a Fuel Cell.

We evaluated the output performance of fuel cells by dipping saidmembrane/electrode assembly I and I′ in deionized boiling water to letthe assemblies absorb water and setting each wet membrane/electrodeassembly in a sample unit. FIG. 1 shows the structure of the sample unitcell of the solid polymer electrolyte fuel cell which comprises saidmembrane/electrode assembly 4 which is prepared by (3) and made up witha polymer electrolyte membrane 1, an oxygen electrode 2 and an hydrogenelectrode 3, current collecting members 5 which are supported and sealedby thin packing material made of carbon paper on the electrodes, andconductive separators 6 (bipolar plates) provided on outer sides of thecurrent collecting members 5 to separate electrodes from the chamber andto supply gasses. The oxygen electrode 2 works as a cathode and thehydrogen electrode 3 works as an anode. Air was passed in a directionfrom the ari inlet 7 to the air outlet 8; fuel (in this case, hydrogen)was passed in a direction from the fuel inlet 9 to fuel outlet 10; andwater yielded by power generation and water accompanied withtransportation of protons was separated in a direction to the wateroutlet 11.

We measured the output voltage of said unit cell of the solid polymerelectrolyte fuel cell while running the unit cell for a long time at acurrent density of 300 mA/cm². FIG. 2 shows the relationship between theoutput voltage and the running time of the unit cell. The curve 12 inFIG. 2 is the result of the endurance test of the unit cell using themembrane/electrode assembly I in accordance with the present invention.The curve 13 in FIG. 2 is the result of the endurance test of the unitcell using the membrane/electrode assembly I′. The curve 14 in FIG. 2 isthe result of the endurance test of the unit cell using aperfluorosulfonic membrane/electrode assembly. As shown by curve 12 inFIG. 2, the output voltage of the membrane/electrode assembly I isinitially 0.8 V and keeps at 0.8 V even after the unit cell runs 5,000hours, which is the same as the behavior of the output voltage of theunit cell using a perfluorosulfonic membrane/electrode assembly (bycurve 14). As shown by curve 15 in FIG. 2, the output voltage (of a unitcell using sulfonated aromatic hydrocarbon electrolyte of Comparativeexample 1 below) is initially 0.73 V but completely exhausted after thefuel cell runs 600 hours. Judging from these, it is apparent that theunit cell of a fuel cell using an aromatic hydrocarbon electrolytehaving a sulfonic group bonded to the aromatic ring via an alkyl groupis more durable than the unit cell of a fuel cell using an aromatichydrocarbon electrolyte having a sulfonic group directly bonded to thearomatic ring. Further, although both membrane/electrode assemblies ofEmbodiment 1 and Comparative example 1 carry 0.25 mg/cm² of platinum,the output voltage of Embodiment 1 is greater than the output voltage ofComparative example 1. This is because the ion conductivities of theelectrolyte and the electrode catalyst covering solution in themembrane/electrode assembly of Embodiment 1 are greater than those ofthe electrolyte and the electrode catalyst covering solution in themembrane/electrode assembly of Comparative example 1 and because themembrane/electrode assembly of Embodiment 1 is superior to themembrane/electrode assembly of Comparative example 1.

(5) Preparation of Fuel Cells

We piled up 36 unit cells which were prepared in (4) to form a solidpolymer electrolyte fuel cell. This fuel cell outputs 3 KW.

COMPARATIVE EXAMPLE 1 (1) Preparation of Sulfonated Polyether Sulfone

We prepared sulfonated polyether sulfone by setting up a 500-ml 4-neckround bottom flask with a reflux condenser, a stirrer, a thermometer,and a desiccant tube (containing calcium chloride in it), substitutingthe air inside the flask by nitrogen gas, putting 25 g ofpolyethersulfone (PES) and 125 ml of concentrated sulfuric acid in theflask, stirring the mixture at a room temperature for one night in thepresence of nitrogen gas to make a uniform solution, dripping 48 ml ofchlorosulfuric acid first slowly (because the chlorosulfuric acidvigorously reacts with water in the sulfuric acid with bubbles) by adropping funnel into the uniform solution in the presence of nitrogengas, completing dripping within 5 minutes after bubbling calms down,stirring the reactant solution at 25° C. for three and half hours tosulfonate thereof, dripping the reactant solution slowly into 15 litersof deionized water, filtering the deionized water to recover theprecipitate (sulfonated poly-ethersulfone), repeating mixing theprecipitate with deionized water and suction-filtering the mixture untilthe filtrate becomes neutral, and vacuum-drying the precipitate at 80°C. for one night. The ion exchange group equivalent weight of theobtained sulfonated poly-ethersulfone electrolyte is 960 g/mol.

We put 1.0 g of obtained sulfonated polyethersulfone electrolyte and 20ml of deionized water in a TEFLON-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured the ion exchange group equivalent weight ofsulfonated polyethersulfone. As the result, we found that the ionexchange group equivalent weight of sulfonated polyethersulfoneelectrolyte is 3,000 g/mol which is greater than the initial ionexchange group equivalent weight (960 g/mol). This means that thesulfonic groups are dissociated.

(2) Preparation of an Electrolyte Membrane

We prepared an electrolyte membrane by dissolving sulfonatedpolyethersulfone electrolyte obtained by the above description (1) intoa mixture of 20 parts of N,N′-dimethylformamide, 80 parts ofcyclohexanon, and 25 parts of methylethylketone so that the solution maycontain 5% by weight of the product, spreading this solution over aglass plate by spin-coating, air-drying thereof, and vacuum-dryingthereof at 80° C. The obtained electrolyte membrane II is 45 μm thickand its ion exchange group equivalent is 0.02 S/cm.

We put said obtained electrolyte membrane II and 20 ml of deionizedwater in a TEFLON-coated hermetic stainless steel container, kept thecontainer at 120° C. for 2 weeks, cooled the container and theninspected thereof. As the result, we found the electrolyte membranebroken and ragged.

(3) Preparation of a Solution for Covering Electrode Catalyst and aMembrane/Electrode Assembly

We prepared a solution II for covering electrode catalyst by adding asolvent mixture of N,N′-dimethylformamide, cyclohexanon, andmethylethylketone which contains 5% by weight of the product (see (2))to carbon carrying 40% by weight of platinum so that the ratio by weightof platinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly II by coating both sides of the electrolyte membrane II(obtained by (2)) with said solution II for covering electrode catalyst,and drying thereof. The obtained embrane/electrode assembly II carries0.25 mg/cm² of platinum.

We put said obtained membrane/electrode assembly II and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and theninspected thereof. As the result, we found the membrane/electrodeassembly II broken and ragged.

(4) Endurance Test of Unit Cells of a Fuel Cell

We assembled the membrane/electrode assembly II of Comparative example1, thin carbon-paper packing materials (as supporting currentcollectors) at both sides of the assembly, and conductive separators(bipolar plates) provided at outer sides thereof and also working toseparate the electrodes from the chamber and to flow gases to theelectrodes into a unit cell for a solid polymer electrolyte fuel cell,and ran the unit cell for a long time at a current density of 300mA/cm². As the result, the output voltage of the unit cell was initially0.73V but exhausted after a 600-hours run, as shown by the curve 15 inFIG. 2.

The cost of the sulfopropyl polyethersulfone electrolyte is one fiftiethof the cost of perfluorosulfonic electrolyte which is prepared fromexpensive material in five processes because the sulfopropyl polyethersulfone electrolyte is prepared in a single process from polyethersulfone which is very cheap engineering plastics on-market.

As seen from Embodiment 1 and Comparative example 1-(1), the cheapsulfopropyl polyethersulfone electrolyte unlike the cheap sulfonatedaromatic hydrocarbon electrolyte (see Comparative example 1 (1)) showsvery good chemical stability as well as the expensive perfluorosulfonicelectrolyte, satisfying both low cost and high performance.

Referring to Embodiment 1 and Comparative examples 1-(1) and 1-(2),although the ion exchange group equivalent weight (980 g/mol) ofEmbodiment 1 (aromatic hydrocarbon electrolyte having a sulfonic groupbonded to the aromatic ring via an alkyl group) is a little greater thanthat (960 g/mol) of Comparative example 1 (aromatic hydrocarbonelectrolyte having a sulfonic group directly bonded to the aromaticring), the ion conductivity of the electrolyte membrane of Embodiment 1is greater than the ion conductivity of the electrolyte membrane ofComparative example 1. (Usually the ion conductivity of an electrolytemembrane is greater as the ion exchange group equivalent weight of theelectrolyte membrane is smaller.) Therefore the electrolyte membrane ofEmbodiment 1 is superior to that of Comparative example 1. Referring toEmbodiment 1 and Comparative examples 1-(2), the cheap sulfopropylpolyethersulfone electrolyte membrane unlike the sulfonated aromatichydrocarbon electrolyte membrane shows very good chemical stability aswell as the expensive perfluorosulfonic electrolyte membrane, satisfyingboth low cost and high performance.

Referring to Embodiment 1 and Comparative examples 1-(3), the cheapsulfopropyl polyethersulfone membrane/electrode assembly unlike thesulfonated aromatic hydrocarbon membrane/electrode assembly shows verygood chemical stability as well as the expensive perfluorosulfonicmembrane/electrode assembly, satisfying both low cost and highperformance.

Referring to Embodiment 1 and Comparative examples 1-(4), the outputvoltage of the unit cell of a fuel cell using the electrode catalystcovering solution of Embodiment 1 is greater than the output voltage ofthe unit cell of a fuel cell using the electrode catalyst coveringsolution of Comparative example 1 and the electrode catalyst coveringsolution of Embodiment 1 is superior to the electrode catalyst coveringsolution of Comparative example 1. The unit cell of a fuel cell of thepresent invention is low cost and as durable as the unit cell of aperfluorosulfonic fuel cell and has substantially high chemicalstability unlike the unit cell of the sulfonated aromatic hydrocarbonfuel cell.

Referring to the curve 12 (for a unit cell of Embodiment 1) of FIG. 2,the output voltage of the membrane/electrode assembly I is initially 0.8V and keeps at 0.8 V even after the unit cell runs 5,000 hours, which isthe same as the behavior of the output voltage of the unit cell using aperfluorosulfonic membrane/electrode assembly (by curve 14). Contrarily,the output of curve 15 (for a unit cell of Comparative example 1) isinitially 0.73 V but completely exhausted after the fuel cell runs 600hours. Judging from these, it is apparent that the unit cell of a fuelcell using an aromatic hydrocarbon electrolyte having a sulfonic groupbonded to the aromatic ring via an alkyl group is more durable than theunit cell of a fuel cell using an aromatic hydrocarbon electrolytehaving a sulfonic group directly bonded to the aromatic ring. Further,although both membrane/electrode assemblies of Comparative examples 1and 2 carry 0.25 mg/cm² of platinum, the output voltage of Embodiment 1is greater than the output voltage of Comparative example 1. This isbecause the ion conductivities of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofEmbodiment 1 are greater than those of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofComparative example 1 and because the membrane/electrode assembly ofEmbodiment 1 is superior to the membrane/electrode assembly ofComparative example 1.

EMBODIMENT 2 (1) Preparation of Sulfopropyl Polyether Etherketone

We prepared sulfopropyl polyether etherketone by setting up a 500-ml4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 14.5 g ofpolyether etherketone, 12.2 g (0.1 mol) of propansultone and 50 ml ofdry nitrobenzene in the flask, adding 14.7 g (0.11 mol) of aluminumchloride anhydride to the mixture gradually for 30 minutes whilestirring thereof, refluxing the mixture for 30 hours after addition ofaluminum chloride anhydride is completed, dripping the reactant solutionslowly into 0.5 liter of deionized water, filtering the deionized waterto recover the precipitate (sulfopropyl polyether etherketone),repeating mixing the precipitate with deionized water andsuction-filtering the mixture until the filtrate becomes neutral, andvacuum-drying the precipitate at 120° C. for one night. The ion exchangegroup equivalent weight of the obtained sulfopropyl polyetheretherketone is 800 g/mol.

The cost of the sulfopropyl polyether etherketone electrolyte is onefortieth of the cost of perfluorosulfonic electrolyte which is preparedfrom expensive material in five processes because the sulfopropylpolyether etherketone electrolyte is prepared in a single process frompoly-ether etherketone which is very cheap engineering plasticson-market.

We put 1.0 g of obtained sulfopropyl polyether etherketone and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured the ion exchange group equivalent weight of sulfopropylpolyether etherketone. As the result, we found that the ion exchangegroup equivalent weight of sulfopropyl polyether etherketone remainsunchanged (800 g/mol) and that sulfopropyl polyether etherketone is asstable as the expensive perfluorosulfonic electrolyte. Contrarily asshown by the comparative example 2-(1) below, the cheap sulfonatedaromatic hydrocarbon electrolyte is deteriorated under the sametemperature and hydrolysis condition. Its ion exchange group equivalentincreases up to 2,500 g/mol (which was initially 600 g/mol) and sulfonegroups were dissociated. In other words, the low-cost sulfopropylpolyether etherketone electrolyte unlike the cheap sulfonated aromatichydrocarbon electrolyte (see Comparative example 2-(1)) shows very goodchemical stability as well as the expensive perfluorosulfonicelectrolyte, satisfying both low cost and high performance.

(2) Preparation of an Electrolyte Membrane

We prepared an electrolyte membrane III by dissolving the productobtained by the above description (1) into a solvent solution ofN-methyl pyrolidone, spreading this solution over a glass plate byspin-coating, air-drying thereof, and vacuum-drying thereof at 80° C.The obtained electrolyte membrane III is 42 μm thick.

We put said obtained electrolyte membrane III and 20 ml of deionizedwater in a TEFLON-coated hermetic stainless steel container, kept thecontainer at 120° C. for 2 weeks, cooled the container and then measuredits ion exchange group equivalent weight. As the result, we found thatthe ion exchange group equivalent weight of the obtained electrolytemembrane remains unchanged as well as the expensive perfluorosulfonicelectrolyte. The membrane itself is tough enough. Contrarily as shown bythe comparative example 2-(2), the comparatively cheap sulfonatedaromatic hydrocarbon electrolyte IV is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropyl polyethersulfone electrolyte unlike the cheap sulfonatedaromatic hydrocarbon electrolyte IV (see Comparative example 2-(2))shows very good chemical stability as well as the expensiveperfluorosulfonic electrolyte, satisfying both low cost and highperformance.

(3) Preparation of a Solution for Covering Electrode Catalyst and aMembrane/Electrode Assembly

We prepared a solution III for covering electrode catalyst by adding aN-methylpyrolidone solution to carbon carrying 40% by weight of platinumso that the ratio by weight of platinum catalyst and the polymerelectrolyte might be 2:1, and dispersing the mixture uniformly. Next weprepared a membrane/electrode assembly III by coating both sides of theelectrolyte membrane III (obtained by (2)) with said solution III forcovering electrode catalyst, and drying thereof. The obtainedmembrane/electrode assembly III carries 0.25 mg/cm² of platinum.

Similarly we prepared a membrane/electrode assembly III′ carrying 0.25mg/cm² of platinum by coating both sides of the electrolyte membrane III(obtained by (2)) with said solution IV for covering electrode catalyststated by Comparative example 2-(3), and drying thereof.

We prepared a paste (a solution for covering electrode catalyst) byadding an alcohol-water mixture of 5% by weight as perfluoro sulfonicelectrolyte to carbon carrying 40% by weight of platinum so that theratio by weight of platinum catalyst and the polymer electrolyte mightbe 2:1, and dispersing the mixture uniformly. Next we coated both sidesof the electrolyte membrane III (obtained by (2)) with this paste(solution). However, the paste could not be uniformly spread over theelectrolyte membrane and we could not get a membrane/electrode assembly.

We put said obtained membrane/electrode assembly and 20 ml of deionizedwater in a TEFLON-coated hermetic stainless steel container and kept thecontainer at 120° C. for 2 weeks. As the result, we found that theobtained electrolyte/membrane assembly III remains unchanged as well asthe membrane/electrode assembly prepared from the expensiveperfluorosulfonic membrane and the perfluorosulfonic electrolyte. Themembrane itself is tough enough

Similarly, we put said obtained membrane/electrode assembly III′ and 20ml of deionized water in a TEFLON-coated hermetic stainless steelcontainer and kept the container at 120° C. for 2 weeks. As the result,we found that the membrane/electrode assembly III′ has enough powergenerating performance although the electrode was partially separated.

Contrarily as shown by the comparative example 2-(3), themembrane/electrode assembly III prepared by comparatively cheapsulfonated aromatic hydrocarbon electrolyte IV and the electrodecatalyst covering solution IV is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropyl polychlorotrifluoroethylene membrane/electrode assemblyunlike the cheap sulfonated aromatic hydrocarbon membrane/electrodeassembly III (see Comparative example 2-(3) is as stable as theexpensive perfluorosulfonic membrane/electrolyte assembly, and satisfiesboth low cost and high performance.

(4) Evaluation of Output of the Unit Cells of a Fuel Cell.

We evaluated the output performance of a fuel cell by dipping saidmembrane/electrode assemblies III and III′ in deionized boiling water tolet the assemblies absorb water and setting each wet membrane/electrodeassembly in a sample unit. FIG. 4 shows a relationship between currentdensity and voltage of a unit cell of a fuel cell containingmembrane/electrode assembly III. The output voltage of the fuel cell is0.6 V at a current density of 1 A/cm² and 0.76 V at a current density or300 mA/^(cm2). This fuel cell is fully available as a solid polymerelectrolyte fuel cell.

We prepared unit cells for solid polymer electrolyte fuel cells byrespectively assembling the membrane/electrode assemblies III and III′of Comparative example 2, thin carbon-paper packing materials (assupporting current collectors) at both sides of the assembly, andconductive separators (bipolar plates) provided at outer sides thereofand also working to separate the electrodes from the chamber and to flowgases to the electrodes into a unit cell for a solid polymer electrolytefuel cell, and ran each unit cell for a long time at a current densityof 300mA/cm². FIG. 5 shows the relationship between the output voltageand the running time of the unit cell. The curve 16 in FIG. 5 is theresult of the endurance test of the unit cell using themembrane/electrode assembly in accordance with the present invention.The curve 17 in FIG. 5 is the result of the endurance test of the unitcell using the membrane/electrode assembly III′. The curve 18 in FIG. 5is the result of the endurance test of the unit cell using aperfluorosulfonic membrane/electrode assembly. As shown by curve 16 inFIG. 5, the output voltage of the unit cell is initially 0.76 V andkeeps at 0.76 V even after the unit cell runs 5,000 hours, which is thesame as the behavior of the output voltage of the unit cell using aperfluorosulfonic membrane (by curve 18). As shown by curve 19 in FIG.5, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example 2 below) is initially0.73 V but completely exhausted after the fuel cell runs 5000 hours.

Judging from these, it is apparent that the unit cell of a fuel cellusing an aromatic hydrocarbon electrolyte having a sulfonic group bondedto the aromatic ring via an alkyl group is more durable than the unitcell of a fuel cell using an aromatic hydrocarbon electrolyte having asulfonic group directly bonded to the aromatic ring. Further, althoughboth membrane/electrode assemblies of Embodiment 2 and Comparativeexample 2 carry 0.25 mg/cm² of platinum, the output voltage ofEmbodiment 2 is greater than the output voltage of Comparative example2. This is because the ion conductivities of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Embodiment 2 are greater than those of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Comparative example 2 and because the membrane/electrode assembly ofEmbodiment 2 is superior to the membrane/electrode assembly ofComparative example 2.

(5) Preparation of Fuel Cells

We piled up 36 unit cells which were prepared in (4) to form a solidpolymer electrolyte fuel cell. This fuel cell outputs 3 KW.

COMPARATIVE EXAMPLE 2 (1) Preparation of Sulfonated PolyetherEtherketone Sulfone

We prepared sulfonated polyether etherketone electrolyte by setting up a500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 6.7 g ofpolyether etherketone (PEEK) and 100 ml of 96% concentrated sulfuricacid in the flask, stirring the mixture at 60° C. for 60 minutes in thepresence of nitrogen gas, adding oleum (containing 20% by weight SO3) tothe solution while stirring the solution in the flow of nitrogen gas tomake 98.5% by weight sulfuric acid, heating the solution at 80° C. for30 minutes, dripping the reactant solution slowly into 15 liters ofdeionized water, filtering the deionized water to recover theprecipitate (sulfonated polyether etherketone), repeating mixing theprecipitate with deionized water and suction-filtering the mixture untilthe filtrate becomes neutral, and vacuum-drying the precipitate at 80°C. for one night. The ion exchange group equivalent weight of theobtained sulfonated polyether etherketone electrolyte is 600 g/mol.

We put 1.0 g of obtained sulfonated polyether etherketone electrolyteand 20 ml of deionized water in a TEFLON-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured the ion exchange group equivalent weight ofsulfonated polyether etherketone. As the result, we found that the ionexchange group equivalent weight of sulfonated polyether etherketoneelectrolyte is 2,500 g/mol which is greater than the initial ionexchange group equivalent weight (960 g/mol). This means that thesulfonic groups are dissociated.

(2) Preparation of an Electrolyte Membrane

We prepared an electrolyte membrane by dissolving sulfonated polyetheretherketone electrolyte obtained by the above description (1) into amixture of 20 parts of N,N′-dimethylformamide, 80 parts of cyclohexanon,and 25 parts of methylethylketone so that the solution may contain 5% byweight of the product, spreading this solution over a glass plate byspin-coating, air-drying thereof, and vacuum-drying thereof at 80° C.The obtained electrolyte membrane IV is 45 μm thick and its ion exchangegroup equivalent is 0.02 S/cm.

We put said obtained electrolyte membrane IV and 20 ml of deionizedwater in a TEFLON-coated hermetic stainless steel container, kept thecontainer at 120° C. for 2 weeks, cooled the container and theninspected thereof. As the result, we found the electrolyte membrane IVbroken and ragged.

(3) Preparation of a Solution for Covering Electrode Catalyst and aMembrane/Electrode Assembly

We prepared a paste (a solution IV for covering electrode catalyst) byadding a solvent mixture of N,N′-dimethylformamide, cyclohexanon, andmethylethylketone which contains 5% by weight of the product (see (2))to carbon carrying 40% by weight of platinum so that the ratio by weightof platinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly IV by coating both sides of the electrolyte membrane IV(obtained by (2)) with said solution IV for covering electrode catalyst,and drying thereof. The obtained membrane/electrode assembly IV carries0.25 mg/cm² of platinum.

We put said obtained membrane/electrode assembly IV and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and theninspected thereof. As the result, we found the membrane/electrodeassembly IV broken and ragged.

(4) Endurance Test of Unit Cells of a Fuel Cell

We prepared a unit cell for a solid polymer electrolyte fuel cell byassembling the membrane/electrode assembly IV of Comparative example 2,thin carbon-paper packing materials (as supporting current collectors)in close contact at both sides of the assembly, and conductiveseparators (bipolar plates) provided at outer sides thereof and alsoworking to separate the electrodes from the chamber and to flow gases tothe electrodes and ran the unit cell for a long time at a currentdensity of 300 mA/cm². As the result, the output voltage of the unitcell was initially 0.73 V but exhausted after a 5,000-hours run, asshown by the curve 19 in FIG. 5.

The cost of the sulfopropyl polyether etherketone electrolyte is onefortieth of the cost of perfluorosulfonic electrolyte which is preparedfrom expensive material in five processes because the sulfopropylpolyether etherketone electrolyte is prepared in a single process frompolyether etherketone which is very cheap engineering plasticson-market.

As seen from Embodiment 2 and Comparative example 2-(1), the aromatichydrocarbon electrolyte (Embodiment 2) having a sulfonic group bonded tothe aromatic ring via an alkyl group is more resistant to the hotdeionized water (120° C. ) than the aromatic hydrocarbon electrolyte(Comparative example 2) having a sulfonic group directly bonded to thearomatic ring.

Referring to Embodiment 1 and Comparative examples 2-(3), the electrodecatalyst covering solution of Embodiment 2 is more suitable for thearomatic hydrocarbon membrane than the perfluorosulfonic electrodecatalyst covering solution. Referring to Embodiment 2 and Comparativeexamples 2-(4), the output voltage of a unit cell using the electrodecatalyst covering solution of Embodiment 2 is greater than the outputvoltage of a unit cell using the electrode catalyst covering solution ofComparative example 2. Therefore, the electrode catalyst coveringsolution of Embodiment 2 is superior to the electrode catalyst coveringsolution of Comparative example 2.

Referring to the curve 16 of FIG. 5, the output voltage of the unit cellof Embodiment 2 is initially 0.8 V and keeps at 0.8 V even after theunit cell runs 5,000 hours, which is the same as the behavior of theoutput voltage of the unit cell using a perfluorosulfonicmembrane/electrode assembly (by curve 18). Contrarily, the output ofcurve 19 (for a unit cell of Comparative example 2) is initially 0.73 Vand completely exhausted after the fuel cell runs 5000 hours. Judgingfrom these, it is apparent that the unit cell of a fuel cell using anaromatic hydrocarbon electrolyte having a sulfonic group bonded to thearomatic ring via an alkyl group is more durable than the unit cell of afuel cell using an aromatic hydrocarbon electrolyte having a sulfonicgroup directly bonded to the aromatic ring. Further, although bothmembrane/electrode assemblies of Embodiment 2 and Comparative examples 2carry 0.25 mg/cm² of platinum, the output voltage of Embodiment 2 isgreater than the output voltage of Comparative example 2. This isbecause the ion conductivities of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofEmbodiment 2 are greater than those of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofComparative example 2 and because the membrane/electrode assembly ofEmbodiment 2 is superior to the membrane/electrode assembly ofComparative example 2.

EMBODIMENT 3 (1) Preparation of Sulfopropyl Poly-Phenylene Sulfide

We prepared sulfopropyl poly-phenylene sulfide by setting up a 500-ml4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 10.8 g ofpoly-phenylene sulfide (PPS), 12.2 g (0.1 mol) of propansultone and 50ml of dry nitrobenzene in the flask, adding 14.7 g (0.11 mol) ofaluminum chloride anhydride to the mixture gradually for 30 minuteswhile stirring thereof, refluxing the mixture for 10 hours afteraddition of aluminum chloride anhydride is completed, dripping thereactant solution slowly into 0.5 liter of deionized water, filteringthe deionized water to recover the precipitate (sulfopropylpoly-phenylene sulfide), repeating mixing the precipitate with deionizedwater and suction-filtering the mixture until the filtrate becomesneutral, and vacuum-drying the precipitate at 120° C. for one night. Theion exchange group equivalent weight of the obtained sulfopropylpoly-phenylene sulfide is 520 g/mol.

The cost of the sulfopropyl poly-phenylene sulfide electrolyte is onefiftieth of the cost of perfluorosulfonic electrolyte which is preparedfrom expensive material in five processes because the sulfopropylpoly-phenylene sulfide electrolyte is prepared in a single process frompoly-phenylene sulfide which is very cheap engineering plasticson-market.

We put 1.0 g of obtained sulfopropyl poly-phenylene sulfide and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured the ion exchange group equivalent weight of sulfopropylpoly-phenylene sulfide. As the result, we found that the ion exchangegroup equivalent weight of sulfopropyl poly-phenylene sulfide remainsunchanged (520 g/mol) and that sulfopropyl poly-phenylene sulfide is asstable as the expensive perfluorosulfonic electrolyte. Contrarily asshown by the comparative example 3-(1) below, the cheap sulfonatedaromatic hydrocarbon electrolyte is deteriorated under the sametemperature and hydrolysis condition. Its ion exchange group equivalentincreases up to 3,500 g/mol (which was initially 500 g/mol) and sulfongroups were dissociated. In other words, the low-cost sulfopropylpoly-phenylene sulfide electrolyte unlike the cheap sulfonated aromatichydrocarbon electrolyte (see Comparative example 3-(1)) shows very goodchemical stability as well as the expensive perfluorosulfonicelectrolyte, satisfying both low cost and high performance.

(2) Preparation of an Electrolyte Membrane

We prepared an electrolyte membrane V by dissolving the product(sulfopropyl poly-phenylene sulfide) obtained by the above description(1) into a solvent solution of N-methyl pyrolidone, spreading thissolution over a glass plate by spin-coating, air-drying thereof, andvacuum-drying thereof at 80° C. The obtained electrolyte membrane V is46 μm thick.

We put said obtained electrolyte membrane V and 20 ml of deionized waterin a TEFLON-coated hermetic stainless steel container, kept thecontainer at 120° C. for 2 weeks, cooled the container and then measuredits ion exchange group equivalent weight. As the result, we found thatthe ion exchange group equivalent weight of the obtained electrolytemembrane remains unchanged as well as the expensive perfluorosulfonicelectrolyte. The membrane itself is tough enough. Contrarily as shown bythe comparative example 3-(2), the comparatively cheap sulfonatedaromatic hydrocarbon electrolyte VI is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropyl poly-phenylene sulfide electrolyte unlike the cheapsulfonated aromatic hydrocarbon electrolyte IV (see Comparative example3-(2)) shows very good chemical stability as well as the expensiveperfluorosulfonic electrolyte, satisfying both low cost and highperformance.

(3) Preparation of a Solution for Covering Electrode Catalyst and aMembrane/Electrode Assembly

We prepared a solution V for covering electrode catalyst by adding aN-methylpyrolidone solution to carbon carrying 40% by weight of platinumso that the ratio by weight of platinum catalyst and the polymerelectrolyte might be 2:1, and dispersing the mixture uniformly. Next wecoated one side of the electrolyte membrane V (obtained by (2)) withsaid electrode catalyst covering solution V, and drying thereof.Further, we prepared a solution V′ for covering electrode catalyst byadding a N-methylpyrolidone solution to carbon carrying 40% by weight ofplatinum-ruthenium alloy so that the ratio by weight ofplatinum-ruthenium alloy catalyst and the polymer electrolyte might be2:1, and dispersing the mixture uniformly. Next we covered the otherside of the membrane V (obtained by (2)) with said electrode catalystcovering solution V′, and drying thereof. Thus we prepared amembrane/electrode assembly V having one side (oxygen electrode) of 0.25mg/cm² of platinum and the other side (hydrogen electrode) of 0.3 mg/cm²of platinum-ruthenium alloy.

In the same manner but using the electrode catalyst covering solution VIof Comparative example 3, we prepared a membrane/electrode assembly V′having one side (oxygen electrode) of 0.25 mg/cm² of platinum and theother side (hydrogen electrode) of 0.3 mg/cm² of platinum-rutheniumalloy.

We prepared a paste (a solution for covering electrode catalyst) byadding an alcohol-water mixture of 5% by weight as perfluoro sulfonicelectrolyte to carbon carrying 40% by weight of platinum so that theratio by weight of platinum catalyst and the polymer electrolyte mightbe 2:1, and dispersing the mixture uniformly. Next we coated both sidesof the electrolyte membrane V (obtained by (2)) with this paste(solution). However, the paste could not be uniformly spread over theelectrolyte membrane and we could not get a membrane/electrode assembly.We put said obtained membrane/electrode assembly V and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the obtained electrolyte/membrane assembly V remains unchanged aswell as the membrane/electrode assembly prepared from the expensiveperfluorosulfonic membrane and the perfluorosulfonic electrolyte. Themembrane itself is tough enough.

Similarly, we put said obtained membrane/electrode assembly V′ and 20 mlof deionized water in a TEFLON-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the membrane/electrode assembly V′ has enough power generatingperformance although the electrode was partially separated.

Contrarily as shown by the comparative example 1-(3), themembrane/electrode assembly VI prepared by comparatively cheapsulfonated aromatic hydrocarbon electrolyte VI and the electrodecatalyst covering solution VI is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropyl polyphenylene sulfide membrane/electrode assembly unlike thecheap sulfonated aromatic hydrocarbon membrane/electrode assembly (seeComparative example 3-(3) is as stable as the expensiveperfluorosulfonic membrane/electrolyte assembly, and satisfies both lowcost and high performance.

(4) Evaluation of Output of the Unit Cells of a Fuel Cell

We evaluated the output performance of a fuel cell by dipping saidmembrane/electrode assembly in deionized boiling water to let theassembly absorb water and setting the wet membrane/electrode assembly ina sample unit. FIG. 6 shows a relationship between current density andvoltage of a unit cell of a fuel cell containing membrane/electrodeassembly VI. The output voltage of the fuel cell is 0.63 V at a currentdensity of 1 A/cm² and 0.78 V at a current density or 300 mA/cm². Thisfuel cell is fully available as a solid polymer electrolyte fuel cell.

We ran the unit cell of said solid polymer electrolyte fuel cell for along time at a current density of 300 mA/cm². FIG. 7 shows therelationship between the output voltage and the running time of the unitcell. The curve 20 in FIG. 7 is the result of the endurance test of theunit cell using the membrane/electrode assembly V in accordance with thepresent invention. The curve 21 in FIG. 7 is the result of the endurancetest of the unit cell using the membrane/electrode assembly V′. Thecurve 22 in FIG. 7 is the result of the endurance test of the unit cellusing a perfluorosulfonic membrane/electrode assembly. As shown by curve20 in FIG. 7, the output voltage of the unit cell is initially 0.78 Vand keeps at 0.78 V even after the unit cell runs 5,000 hours, which isthe same as the behavior of the output voltage of the unit cell using aperfluorosulfonic membrane (by curve 22). As shown by curve 23 in FIG.7, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example 3 below) is initially0.63 V but completely exhausted after the fuel cell runs 600 hours.Judging from these, it is apparent that the unit cell of a fuel cellusing an aromatic hydrocarbon electrolyte having a sulfonic group bondedto the aromatic ring via an alkyl group is more durable than the unitcell of a fuel cell using an aromatic hydrocarbon electrolyte having asulfonic group directly bonded to the aromatic ring.

Further, although both membrane/electrode assemblies of Embodiment 3 andComparative example 3 carry 0.25 mg/cm² of platinum, the output voltageof Embodiment 3 is greater than the output voltage of Comparativeexample 3. This is because the ion conductivities of the electrolyte andthe electrode catalyst covering solution in the membrane/electrodeassembly of Embodiment 3 are greater than those of the electrolyte andthe electrode catalyst covering solution in the membrane/electrodeassembly of Comparative example 3 and because the membrane/electrodeassembly of Embodiment 3 is superior to the membrane/electrode assemblyof Comparative example 3.

(5) Preparation of Fuel Cells

We piled up 36 unit cells which were prepared in (4) to form a solidpolymer electrolyte fuel cell. This fuel cell outputs 3 KW.

COMPARATIVE EXAMPLE 3 (1) Preparation of Sulfonated Poly-PhenyleneSulfide

We prepared sulfonated poly-phenylene sulfide by setting up a 500-ml4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 12 g ofpoly-phenylene sulfide (PPS) and 220 ml of chlorosulfuric acid, stirringthe mixture for 30 minutes at 5° C. in the flow of a nitrogen gas todissolve PPS, keeping still at 20° C. for 150 minutes and at 50° C. for60 minutes, dripping the reactant solution slowly into 15 liters ofdeionized water, filtering the deionized water to recover theprecipitate (sulfonated poly-phenylene sulfide), repeating mixing theprecipitate with deionized water and suction-filtering the mixture untilthe filtrate becomes neutral, and vacuum-drying the precipitate at 80°C. for one night. The ion exchange group equivalent weight of theobtained sulfonated poly-phenylene sulfide is 500 g/mol.

We put 1.0 g of obtained sulfonated polyether sulfone and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured the ion exchange group equivalent weight of sulfonatedpoly-phenylene sulfide. As the result, we found that the ion exchangegroup equivalent weight of sulfonated poly-phenylene sulfide is 3,500g/mol which is greater than the initial ion exchange group equivalentweight. This means that the sulfonic groups are dissociated.

(2) Preparation of an Electrolyte Membrane

We prepared a sulfonated poly-phenylene sulfide electrolyte membrane bydissolving sulfonated poly-phenylene sulfide electrolyte obtained by theabove description (1) into a mixture of 20 parts ofN,N′-dimethylformamide, 80 parts of cyclohexanon, and 25 parts ofmethylethylketone, spreading this solution over a glass plate byspin-coating, air-drying thereof, and vacuum-drying thereof at 80° C.The obtained sulfonated poly-phenylene sulfide electrolyte membrane VIis 45 μm thick and its ion exchange group equivalent is 0.02 S/cm.

We put said sulfonated poly-phenylene sulfide electrolyte membrane VIand 20 ml of deionized water in a TEFLON-coated hermetic stainless steelcontainer and kept the container at 120° C. for 2 weeks. As the result,we found the sulfonated poly-phenylene sulfide electrolyte membrane VIbroken and ragged.

(3) Preparation of a Solution for Covering Electrode Catalyst and aMembrane/Electrode Assembly

We prepared a paste (a solution VI for covering electrode catalyst) byadding a solvent mixture of N,N′-dimethylformamide, cyclohexanon, andmethylethylketone which contains 5% by weight of the product (see (2))to carbon carrying 40% by weight of platinum so that the ratio by weightof platinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly VI by coating both sides of the electrolyte membrane VI(obtained by (2)) with said solution VI for covering electrode catalyst,and drying thereof. The obtained membrane/electrode assembly IV carries0.25 mg/cm² of platinum.

We put said obtained membrane/electrode assembly VI and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and theninspected thereof. As the result, we found the membrane/electrodeassembly VI broken and ragged.

(4) Endurance Test of Unit Cells of a Fuel Cell

We prepared a unit cell for a solid polymer electrolyte fuel cell byassembling the membrane/electrode assembly VI of Comparative example 3,thin carbon-paper packing materials (as supporting current collectors)in close contact at both sides of the assembly, and conductiveseparators (bipolar plates) provided at outer sides thereof and alsoworking to separate the electrodes from the chamber and to flow gases tothe electrodes and ran the unit cell for a long time at a currentdensity of 300 mA/cm².

As the result, the output voltage of the unit cell was initially 0.63 Vbut exhausted after a 600-hours run, as shown by the curve 23 in FIG. 7.

The cost of the sulfonated poly-phenylene sulfide electrolyte is onefiftieth of the cost of perfluorosulfonic electrolyte which is preparedfrom expensive material in five processes because the sulfonatedpoly-phenylene sulfide electrolyte is prepared in a single process frompoly-phenylene sulfide which is very cheap engineering plasticson-market.

As seen from Embodiment 3 and Comparative example 3-(1), the aromatichydrocarbon electrolyte (Embodiment 3) having a sulfonic group bonded tothe aromatic ring via an alkyl group is more resistant to the hotdeionized water (120° C. ) than the aromatic hydrocarbon electrolyte(Comparative example 3) having a sulfonic group directly bonded to thearomatic ring.

Referring to Embodiment 3 and Comparative examples 3-(1) and 3-(2),although the ion exchange group equivalent weight (520 g/mol) ofEmbodiment 3 (aromatic hydrocarbon electrolyte having a sulfonic groupbonded to the aromatic ring via an alkyl group) is a little greater thanthat (500 g/mol) of Comparative example 3 (aromatic hydrocarbonelectrolyte having a sulfonic group directly bonded to the aromaticring), the ion conductivity of the electrolyte membrane of Embodiment 3is greater than the ion conductivity of the electrolyte membrane ofComparative example 3. (Usually the ion conductivity of an electrolytemembrane is greater as the ion exchange group equivalent weight of theelectrolyte membrane is smaller.) Therefore the electrolyte membrane ofEmbodiment 3 is superior to that of Comparative example 3.

Referring to Embodiment 3 and Comparative examples 3-(3), the electrodecatalyst covering solution of Embodiment 3 is more suitable for thearomatic hydrocarbon membrane than the perfluorosulfonic electrodecatalyst covering solution. Referring to Embodiment 3 and Comparativeexamples 3-(4), the output voltage of a unit cell using the electrodecatalyst covering solution of Embodiment 3 is greater than the outputvoltage of a unit cell using the electrode catalyst covering solution ofComparative example 3. Therefore, the electrode catalyst coveringsolution of Embodiment 3 is superior to the electrode catalyst coveringsolution of Comparative example 3.

Referring to the curve 20 of FIG. 7, the output voltage of the unit cellof Embodiment 3 is initially 0.78 V and keeps at 0.78 V even after theunit cell runs 5,000 hours, which is the same as the behavior of theoutput voltage of the unit cell using a perfluorosulfonicmembrane/electrode assembly (by curve 22). Contrarily, the output ofcurve 23 (for a unit cell of Comparative example 3) is initially 0.63 Vand completely exhausted after the fuel cell runs 600 hours. Judgingfrom these, it is apparent that the unit cell of a fuel cell using anaromatic hydrocarbon electrolyte having a sulfonic group bonded to thearomatic ring via an alkyl group is more durable than the unit cell of afuel cell using an aromatic hydrocarbon electrolyte having a sulfonicgroup directly bonded to the aromatic ring. Further, although bothmembrane/electrode assemblies of Embodiment 3 and Comparative examples 3carry 0.25 mg/cm² of platinum, the output voltage of Embodiment 3 isgreater than the output voltage of Comparative example 3. This isbecause the ion conductivities of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofEmbodiment 3 are greater than those of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofComparative example 3 and because the membrane/electrode assembly ofEmbodiment 3 is superior to the membrane/electrode assembly ofComparative example 3.

EMBODIMENT 4 (1) Preparation of Sulfopropyl Reformed Polyphenylene Oxide

We prepared sulfopropyl reformed polyphenylene oxide by setting up a500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 12.0 g ofpolyphenylene oxide (m-PPE), 12.2 g (0.1 mol) of propansultone and 50 mlof dimethyl sulfoxide, adding 14.7 g (0.11 mol) of aluminum chlorideanhydride to the mixture gradually for 30 minutes while stirringthereof, keeping the mixture at 150° C. for 8 hours, dripping thereactant solution into 500 ml of iced water containing 25 ml ofconcentrated hydrochloric acid to stop the reaction, separating theorganic precipitate, washing thereof, neutralizing thereof with anaqueous solution of sodium carbonate containing a few drops of octylalcohol, separating aluminum hydroxide by filtration, decoloring thefiltrate by active carbon, and evaporating the solvent. The ion exchangegroup equivalent weight of the obtained sulfopropyl reformedpolyphenylene oxide is 370 g/mol. The cost of the sulfopropylpolyphenylene oxide electrolyte is one fiftieth of the cost ofperfluorosulfonic electrolyte which is prepared from expensive materialin five processes because the sulfopropyl polyphenylene oxideelectrolyte is prepared in a single process from polyphenylene oxidewhich is very cheap engineering plastics on-market.

We put 1.0 g of said sulfopropyl reformed polyphenylene oxide and 20 mlof deionized water in a TEFLON-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured the ion exchange group equivalent weight ofthe sulfopropyl reformed polyphenylene oxide electrolyte. As the result,we found that the ion exchange group equivalent weight of sulfopropylreformed polyphenylene oxide remains unchanged (520 g/mol) and thatsulfopropyl reformed polyphenylene oxide is as stable as the expensiveperfluorosulfonic electrolyte. Contrarily as shown by the comparativeexample 4-(1) below, the cheap sulfonated aromatic hydrocarbonelectrolyte is deteriorated under the same temperature and hydrolysiscondition. Its ion exchange group equivalent increases up to 3,500 g/mol(which was initially 490 g/mol) and sulfone groups were dissociated. Inother words, the low-cost sulfopropyl reformed polyphenylene oxideelectrolyte unlike the cheap sulfonated aromatic hydrocarbon electrolyte(see Comparative example 4-(1)) shows very good chemical stability aswell as the expensive perfluorosulfonic electrolyte, satisfying both lowcost and high performance.

(2) Preparation of an Electrolyte Membrane

We prepared a sulfopropyl reformed polyphenylene oxide electrolytemembrane by dissolving sulfopropyl reformed polyphenylene oxideelectrolyte obtained by the above description (1) into a mixture of 20parts of N,N′-dimethylformamide, 80 parts of cyclohexanon, and 25 partsof methylethylketone so that the solution may contain 5% by weight ofthe product, spreading this solution over a glass plate by spin-coating,air-drying thereof, and vacuum-drying thereof at 80° C. The obtainedsulfopropyl reformed polyphenylene oxide electrolyte membrane VII is 42μm thick and its ion exchange group equivalent is 0.01 S/cm.

We put said obtained electrolyte membrane VII and 20 ml of deionizedwater in a TEFLON-coated hermetic stainless steel container and kept thecontainer at 120° C. for 2 weeks. As the result, we found that the ionexchange group equivalent weight of the obtained electrolyte membraneremains unchanged as well as the expensive perfluorosulfonicelectrolyte. The membrane itself is tough enough. Contrarily as shown bythe comparative example 4-(2), the comparatively cheap sulfonatedaromatic hydrocarbon electrolyte VIII is broken and ragged under thesame temperature and hydrolysis condition. In other words, the low-costsulfopropyl reformed polyphenylene oxide electrolyte unlike the cheapsulfonated aromatic hydrocarbon electrolyte (see Comparative example4-(2)) shows very good chemical stability as well as the expensiveperfluorosulfonic electrolyte, satisfying both low cost and highperformance.

(3) Preparation of a Solution for Covering Electrode Catalyst and aMembrane/Electrode Assembly

We prepared a paste (a solution VII for covering electrode catalyst) byadding a solvent mixture of N,N′-dimethylformamide, cyclohexanon, andmethylethylketone which contains 5% by weight of the product (see (2))to carbon carrying 40% by weight of platinum so that the ratio by weightof platinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly IV by coating both sides of the electrolyte membrane VII(obtained by (2)) with said solution VII for covering electrodecatalyst, and drying thereof. The obtained membrane/electrode assemblyVII carries 0.25 mg/cm² of platinum.

We put said obtained membrane/electrode assembly VI and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the obtained electrolyte/membrane assembly VII remains unchanged aswell as the membrane/electrode assembly prepared from the expensiveperfluorosulfonic membrane and the perfluorosulfonic electrolyte. Themembrane itself is tough enough.

Contrarily as shown by the comparative example 4-(3), themembrane/electrode assembly VIII prepared by comparatively cheapsulfonated aromatic hydrocarbon electrolyte VIII and the electrodecatalyst covering solution VIII is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropyl reformed polyphenylene oxide membrane/electrode assemblyunlike the cheap sulfonated aromatic hydrocarbon membrane/electrodeassembly (see Comparative example 4-(3)) is as stable as the expensiveperfluorosulfonic membrane/electrolyte assembly, and satisfies both lowcost and high performance.

(4) Evaluation of Output of the Unit Cells of a Fuel Cell

We evaluated the output performance of a fuel cell by dipping saidmembrane/electrode assembly VII in deionized boiling water to let theassembly absorb water and setting the wet membrane/electrode assembly ina sample unit. FIG. 8 shows a relationship between current density andvoltage of a unit cell of a fuel cell containing membrane/electrodeassembly VII. The output voltage of the fuel cell is 0.69 V at a currentdensity of 1 A/cm² and 0.82 V at a current density or 300 mA/cm². Thisfuel cell is fully available as a solid polymer electrolyte fuel cell.We ran said unit cell for a long time at a current density of 300mA/cm². FIG. 9 shows the relationship between the output voltage and therunning time of the unit cell. The curve 24 in FIG. 9 is the result ofthe endurance test of the unit cell using the membrane/electrodeassembly VII in accordance with the present invention. The curve 25 inFIG. 9 is the result of the endurance test of the unit cell using aperfluorosulfonic membrane/electrode assembly. As shown by curve 24 inFIG. 9, the output voltage of the unit cell is initially 0.82 V andkeeps at the voltage level even after the unit cell runs 5,000 hours,which is the same as the behavior of the output voltage of the unit cellusing a perfluorosulfonic membrane (by curve 25). As shown by curve 26in FIG. 9, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example 4 below) is initially0.63 V but completely exhausted after the fuel cell runs 600 hours.Judging from these, it is apparent that the unit cell of a fuel cellusing an aromatic hydrocarbon electrolyte having a sulfonic group bondedto the aromatic ring via an alkyl group is more durable than the unitcell of a fuel cell using an aromatic hydrocarbon electrolyte having asulfonic group directly bonded to the aromatic ring. Further, althoughboth membrane/electrode assemblies of Embodiment 4 and Comparativeexample 4 carry 0.25 mg/cm² of platinum, the output voltage ofEmbodiment 4 is greater than the output voltage of Comparative example4. This is because the ion conductivities of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Embodiment 4 are greater than those of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Comparative example 4 and because the membrane/electrode assembly ofEmbodiment 2 is superior to the membrane/electrode assembly ofComparative example 4.

(5) Preparation of Fuel Cells

We piled up 36 unit cells which were prepared in (4) to form a solidpolymer electrolyte fuel cell. This fuel cell outputs 3 KW.

COMPARATIVE EXAMPLE 4 (1) Preparation of Sulfonated ReformedPoly-Phenylene Oxide

We prepared sulfonated reformed poly-phenylene oxide by setting up a500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 12 g ofpoly-phenylene oxide (m-PPE) and 220 ml of chlorosulfuric acid, stirringthe mixture for 30 minutes at 5° C. in the flow of a nitrogen gas todissolve PPS, keeping still at 20° C. for 150 minutes and at 50° C. for60 minutes, dripping the reactant solution slowly into 15 liters ofdeionized water, filtering the deionized water to recover theprecipitate (sulfonated reformed poly-phenylene oxide), repeating mixingthe precipitate with deionized water and suction-filtering the mixtureuntil the filtrate becomes neutral, and vacuum-drying the precipitate at80° C. for one night. The ion exchange group equivalent weight of theobtained sulfonated reformed poly-phenylene oxide is 490 g/mol.

We put 1.0 g of obtained sulfonated reformed poly-phenylene oxideelectrolyte and 20 ml of deionized water in a TEFLON-coated hermeticstainless steel container, kept the container at 120° C. for 2 weeks,cooled the container and then measured the ion exchange group equivalentweight of the sulfonated reformed poly-phenylene oxide electrolyte. Asthe result, we found that the ion exchange group equivalent weight ofsulfonated reformed poly-phenylene oxide is 3,500 g/mol which is greaterthan the initial ion exchange group equivalent weight. This means thatthe sulfonic groups are dissociated.

(2) Preparation of an Electrolyte Membrane

We prepared a sulfonated reformed poly-phenylene oxide electrolytemembrane by dissolving the product obtained by the above procedure (1)into a mixture of 20 parts of N,N′-dimethylformamide, 80 parts ofcyclohexanon, and 25 parts of methylethylketone so that the solution maycontain 5% by weight of the product, spreading this solution over aglass plate by spin-coating, air-drying thereof, and vacuum-dryingthereof at 80° C. The obtained sulfonated reformed poly-phenylene oxideelectrolyte membrane VIII is 45 μm thick and its ion exchange groupequivalent is 0.02 S/cm.

We put said sulfonated reformed poly-phenylene oxide electrolytemembrane VIII and 20 ml of deionized water in a TEFLON-coated hermeticstainless steel container and kept the container at 120° C. for 2 weeks.As the result, we found the sulfonated reformed poly-phenylene oxideelectrolyte membrane VIII broken and ragged.

(3) Preparation of a Solution for Covering Electrode Catalyst and aMembrane/Electrode Assembly

We prepared a paste (a solution VIII for covering electrode catalyst) byadding a solvent mixture of N,N′-dimethylformamide, cyclohexanon, andmethylethylketone which contains 5% by weight of the product (see (2))to carbon carrying 40% by weight of platinum so that the ratio by weightof platinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly VIII by coating both sides of the sulfonated reformedpoly-phenylene oxide electrolyte membrane VIII (obtained by (2)) withsaid electrode covering solution VIII, and drying thereof. The obtainedmembrane/electrode assembly VIII carries 0.25 mg/cm² of platinum.

We put said obtained membrane/electrode assembly VIII and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthe membrane/electrode assembly VIII broken and ragged.

(4) Endurance Test of Unit Cells of a Fuel Cell

We prepared a unit cell for a solid polymer electrolyte fuel cell byassembling the membrane/electrode assembly VII of Comparative example 4,thin carbon-paper packing materials (as supporting current collectors)in close contact at both sides of the assembly, and conductiveseparators (bipolar plates) provided at outer sides thereof and alsoworking to separate the electrodes from the chamber and to flow gases tothe electrodes and ran the unit cell for a long time at a currentdensity of 300 mA/cm². As the result, the output voltage of the unitcell was initially 0.63V but exhausted after a 600-hours run, as shownby the curve 26 in FIG. 9.

The cost of the sulfopropylated poly-phenylene oxide electrolyte is onefiftieth of the cost of perfluorosulfonic electrolyte which is preparedfrom expensive material in five processes because the sulfopropylatedpoly-phenylene oxide electrolyte electrolyte is prepared in a singleprocess from poly-phenylene oxide which is very cheap engineeringplastics on-market.

As seen from Embodiment 4 and Comparative example 4-(1), the aromatichydrocarbon electrolyte (Embodiment 4) having a sulfonic group bonded tothe aromatic ring via an alkyl group is more resistant to the hotdeionized water (120° C. ) than the aromatic hydrocarbon electrolyte(Comparative example 3) having a sulfonic group directly bonded to thearomatic ring.

Referring to Embodiment 4 and Comparative examples 4-(1) and 4-(2),although the ion exchange group equivalent weight (520 g/mol) ofEmbodiment 4 (aromatic hydrocarbon electrolyte having a sulfonic groupbonded to the aromatic ring via an alkyl group) is a little greater thanthat (490 g/mol) of Comparative example 4 (aromatic hydrocarbonelectrolyte having a sulfonic group directly bonded to the aromaticring), the ion conductivity of the electrolyte membrane of Embodiment 4is greater than the ion conductivity of the electrolyte membrane ofComparative example 4. (Usually the ion conductivity of an electrolytemembrane is greater as the ion exchange group equivalent weight of theelectrolyte membrane is smaller.) Therefore the electrolyte membrane ofEmbodiment 4 is superior to that of Comparative example 4.

Referring to Embodiment 4 and Comparative examples 4-(3), the electrodecatalyst covering solution of Embodiment 4 is more suitable for thearomatic hydrocarbon membrane than the perfluorosulfonic electrodecatalyst covering solution.

Referring to Embodiment 4 and Comparative examples 4-(4), the outputvoltage of a unit cell using the electrode catalyst covering solution ofEmbodiment 4 is greater than the output voltage of a unit cell using theelectrode catalyst covering solution of Comparative example 4.Therefore, the electrode catalyst covering solution of Embodiment 4 issuperior to the electrode catalyst covering solution of Comparativeexample 4.

Referring to the curve 24 of FIG. 9, the output voltage of the unit cellof Embodiment 4 is initially 0.82 V and keeps at the same voltage leveleven after the unit cell runs 5,000 hours, which is the same as thebehavior of the output voltage of the unit cell using aperfluorosulfonic membrane/electrode assembly (by curve 25). Contrarily,the output of curve 26 (for a unit cell of Comparative example 4) isinitially 0.63 V and completely exhausted after the fuel cell runs 600hours. Judging from these, it is apparent that the unit cell of a fuelcell using an aromatic hydrocarbon electrolyte having a sulfonic groupbonded to the aromatic ring via an alkyl group is more durable than theunit cell of a fuel cell using an aromatic hydrocarbon electrolytehaving a sulfonic group directly bonded to the aromatic ring. Further,although both membrane/electrode assemblies of Embodiment 4 andComparative examples 4 carry 0.25 mg/cm² of platinum, the output voltageof Embodiment 4 is greater than the output voltage of Comparativeexample 4. This is because the ion conductivities of the electrolyte andthe electrode catalyst covering solution in the membrane/electrodeassembly of Embodiment 4 are greater than those of the electrolyte andthe electrode catalyst covering solution in the membrane/electrodeassembly of Comparative example 4 and because the membrane/electrodeassembly of Embodiment 4 is superior to the membrane/electrode assemblyof Comparative example 4.

EMBODIMENT 5 (1) Preparation of Sulfopropylated Polyether Sulfone

We prepared sulfopropylated polyether sulfone by setting up a 500-ml4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 11.6 g ofpolyether sulfone (PES), 12.2 g (0.1 mol) of propanesultone and 50 ml ofdry acetophenone in the flask, adding 14.7 g (0.11 mol) of aluminumchloride anhydride to the mixture gradually for 30 minutes whilestirring thereof, refluxing the mixture for 8 hours after addition ofaluminum chloride anhydride is completed, dripping the reactant solutionslowly into 0.5 liter of deionized water, filtering the deionized waterto recover the precipitate (sulfopropylated polyether sulfone),repeating mixing the precipitate with deionized water andsuction-filtering the mixture until the filtrate becomes neutral, andvacuum-drying the precipitate at 120° C. for one night. The ion exchangegroup equivalent weight of the obtained sulfopropylated polyethersulfone is 700 g/mol.

The cost of the sulfopropylated polyether sulfone electrolyte is onefiftieth or under of the cost of perfluorosulfonic electrolyte which isprepared from expensive material in five processes because thesulfopropylated polyether sulfone electrolyte is prepared in a singleprocess from poly-ether sulfone which is very cheap engineering plasticson-market.

We put 1.0 g of obtained sulfopropylated polyether sulfone and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured the ion exchange group equivalent weight of sulfopropylatedpolyether sulfone. As the result, we found that the ion exchange groupequivalent weight of sulfopropylated polyether sulfone remains unchanged(700 g/mol) and that sulfopropylated polyether sulfone is as stable asthe expensive perfluorosulfonic electrolyte. Contrarily as shown by thecomparative example 1-(1) below, the cheap sulfonated aromatichydrocarbon electrolyte is deteriorated under the same temperature andhydrolysis condition. Its ion exchange group equivalent increases up to3,000 g/mol (which was initially 960 g/mol) and sulfone groups weredissociated. In other words, the low-cost sulfopropylated polyethersulfone electrolyte unlike the cheap sulfonated aromatic hydrocarbonelectrolyte (see Comparative example 1-(1)) shows very good chemicalstability as well as the expensive perfluorosulfonic electrolyte,satisfying both low cost and high performance.

(2) Preparation of an Electrolyte Membrane

We prepared an electrolyte membrane IX by dissolving the productobtained by the above procedure (1) into a solvent solution ofN,N′-dimethyl formamide, spreading this solution over a glass plate byspin-coating, air-drying thereof, and vacuum-drying thereof at 80° C.The obtained electrolyte membrane IX is 40 μm thick.

We put said obtained electrolyte membrane IX and 20 ml of deionizedwater in a TEFLON-coated hermetic stainless steel container and kept thecontainer at 120° C. for 2 weeks. As the result, we found that the ionexchange group equivalent weight of the obtained electrolyte membrane IXremains unchanged as well as the expensive perfluorosulfonicelectrolyte. The membrane itself is tough enough. Contrarily as shown bythe comparative example 1-(2), the comparatively cheap sulfonatedaromatic hydrocarbon electrolyte II is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropyl polyethersulfone electrolyte unlike the cheap sulfonatedaromatic hydrocarbon electrolyte (see Comparative example 1-(2)) showsvery good chemical stability as well as the expensive perfluorosulfonicelectrolyte, satisfying both low cost and high performance.

(3) Preparation of a Solution for Covering Electrode Catalyst and aMembrane/Electrode Assembly

We prepared a solution IX for covering electrode catalyst by adding aN,N′-dimethyl formamide solution to carbon carrying 40% by weight ofplatinum so that the ratio by weight of platinum catalyst and thepolymer electrolyte might be 2:1, and dispersing the mixture uniformly.Next we coated one side of the electrolyte membrane IX (obtained by (2))with said electrode catalyst covering solution IX, and drying thereof.Further, we prepared a solution IX′ for covering electrode catalyst byadding a N,N′-dimethyl formamide solution to carbon carrying 40% byweight of platinum-ruthenium alloy so that the ratio by weight ofplatinum-ruthenium alloy catalyst and the polymer electrolyte might be2:1, and dispersing the mixture uniformly. Next we covered the otherside of the membrane IX (obtained by (2)) with said electrode catalystcovering solution IX′, and drying thereof. Thus we prepared amembrane/electrode assembly IX having one side (oxygen electrode) of0.29 mg/cm² of platinum and the other side (hydrogen electrode) of 0.32mg/cm² of platinum-ruthenium alloy.

We put said obtained membrane/electrode assembly IX and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the obtained electrolyte/membrane assembly IX remains unchanged aswell as the membrane/electrode assembly prepared from the expensiveperfluorosulfonic membrane and the perfluorosulfonic electrolyte. Themembrane itself is tough enough.

Contrarily as shown by the comparative example 1-(3), themembrane/electrode assembly II prepared by comparatively cheapsulfonated aromatic hydrocarbon electrolyte II and the electrodecatalyst covering solution II is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropylated polyether sulfone membrane/electrode assembly unlike thecheap sulfonated aromatic hydrocarbon membrane/electrode assembly (seeComparative example 1-(3) is as stable as the expensiveperfluorosulfonic membrane/electrolyte assembly, and satisfies both lowcost and high performance.

(4) Evaluation of Output of the Unit Cells of a Fuel Cell

We evaluated the output performance of a fuel cell by dipping saidmembrane/electrode assembly IX in deionized boiling water for 2 hours tolet the assembly absorb water and setting the wet membrane/electrodeassembly in a sample unit. FIG. 10 shows a relationship between currentdensity and voltage of a unit cell of a fuel cell containingmembrane/electrode assembly IX. The output voltage of the fuel cell is0.63 V at a current density of 1 A/cm² and 0.80 V at a current densityor 300 mA/cm². This fuel cell is fully available as a solid polymerelectrolyte fuel cell.

We ran the unit cell of said solid polymer electrolyte fuel cell for along time at a current density of 300 mA/cm². FIG. 11 shows therelationship between the output voltage and the running time of the unitcell. The curve 27 in FIG. 11 is the result of the endurance test of theunit cell using the membrane/electrode assembly IX in accordance withthe present invention. The curve 28 in FIG. 11 is the result of theendurance test of the unit cell using a perfluorosulfonicmembrane/electrode assembly. As shown by curve 27 in FIG. 11, the outputvoltage of the unit cell is initially 0.80 V and keeps at the samevoltage level even after the unit cell runs 5,000 hours, which is thesame as the behavior of the output voltage of the unit cell using aperfluorosulfonic membrane (by curve 28). As shown by curve 29 in FIG.11, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example 1 below) is initially0.63 V but completely exhausted after the fuel cell runs 600 hours.Judging from these, it is apparent that the unit cell of a fuel cellusing an aromatic hydrocarbon electrolyte having a sulfonic group bondedto the aromatic ring via an alkyl group is more durable than the unitcell of a fuel cell using an aromatic hydrocarbon electrolyte having asulfonic group directly bonded to the aromatic ring.

(5) Preparation of Fuel Cells

We piled up 36 unit cells which were prepared in (4) to form a solidpolymer electrolyte fuel cell as that shown in FIG. 3. This fuel celloutputs 3 KW.

EMBODIMENT 6 (1) Preparation of Sulfopropylated Polysulfone

We prepared sulfopropylated polysulfone electrolyte by setting up a500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 22.1 g ofpolysulfone (PSU), 12.2 g (0.1 mol) of propanesultone and 50 ml of a drysolvent mixture of tricloroethane-dichloroethane (1:1), adding 14.7 g(0.11 mol) of aluminum chloride anhydride to the mixture gradually for30 minutes while stirring thereof, keeping the mixture at 100° C. for 24hours, dripping the reactant solution into 500 ml of iced watercontaining 25 ml of concentrated hydrochloric acid to stop the reaction,separating the organic precipitate, washing thereof, neutralizingthereof with an aqueous solution of sodium carbonate containing a fewdrops of octyl alcohol, separating aluminum hydroxide by filtration,decoloring the filtrate by active carbon, and evaporating the solvent.The ion exchange group equivalent weight of the obtained sulfopropylatedpolysulfone electrolyte is 750 g/mol.

The cost of the sulfopropylated sulfone electrolyte is one fiftieth orunder of the cost of perfluorosulfonic electrolyte which is preparedfrom expensive material in five processes because the sulfopropylatedsulfone electrolyte is prepared in a single process from poly-sulfonewhich is very cheap engineering plastics on-market.

We put 1.0 g of obtained sulfopropylated polysulfone and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured the ion exchange group equivalent weight of the resiltingsulfopropylated polysulfone electrolyte. As the result, we found thatthe ion exchange group equivalent weight of sulfopropylated sulfoneremains unchanged (750 g/mol) and that sulfopropylated sulfone is asstable as the expensive perfluorosulfonic electrolyte. Contrarily asshown by the comparative example 5-(1) below, the cheap sulfonatedaromatic hydrocarbon electrolyte is deteriorated under the sametemperature and hydrolysis condition. Its ion exchange group equivalentincreases up to 3,000 g/mol (which was initially 700 g/mol) and sulfonegroups were dissociated. In other words, the low-cost sulfopropylatedsulfone electrolyte unlike the cheap sulfonated aromatic hydrocarbonelectrolyte (see Comparative example 5-(1)) shows very good chemicalstability as well as the expensive perfluorosulfonic electrolyte,satisfying both low cost and high performance.

(2) Preparation of an Electrolyte Membrane

We prepared an electrolyte membrane by dissolving the sulfopropylatedpolysulfone electrolyte obtained by the above procedure (1) into amixture of trichloroethane and dichloroethane (1:1) so that the solutionmay contain 5% by weight of the product, spreading this solution over aglass plate by spin-coating, air-drying thereof, and vacuum-dryingthereof at 80° C. The obtained sulfopropylated polysulfone electrolytemembrane X is 42 μm thick.

We put said obtained sulfopropylated polysulfone electrolyte membrane Xand 20 ml of deionized water in a TEFLON-coated hermetic stainless steelcontainer, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured its ion exchange group equivalent weight. Asthe result, we found that the ion exchange group equivalent weight ofthe obtained electrolyte membrane remains unchanged as well as theexpensive perfluorosulfonic electrolyte. The membrane itself is toughenough. Contrarily as shown by the comparative example 5-(2), thecomparatively cheap sulfonated aromatic hydrocarbon electrolyte XI isbroken and ragged under the same temperature and hydrolysis condition.In other words, the low-cost sulfopropylated polysulfone electrolyteunlike the cheap sulfonated aromatic hydrocarbon electrolyte (seeComparative example 5-(2)) shows very good chemical stability as well asthe expensive perfluorosulfonic electrolyte, satisfying both low costand high performance.

(3) Preparation of a Solution for Covering Electrode Catalyst and aMembrane/Electrode Assembly

We prepared a solution X for covering electrode catalyst by adding asolvent mixture of trichloroethane and dichloroethane (see (2)) tocarbon carrying 40% by weight of platinum so that the ratio by weight ofplatinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly X by coating both sides of the electrolyte membrane X (obtainedby (2)) with said solution X for covering electrode catalyst, and dryingthereof. The obtained membrane/electrode assembly X carries 0.25 mg/cm²of platinum.

We put said obtained membrane/electrode assembly X and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel containerand kept the container at 120° C. for 2 weeks. As the result, we foundthat the ion exchange group equivalent weight of the obtainedelectrolyte membrane remains unchanged as well as the membrane/electrodeassembly prepared from the expensive perfluorosulfonic membrane and theperfluorosulfonic electrolyte. The membrane itself is tough enough.

Contrarily as shown by the comparative example 5-(3), themembrane/electrode assembly XI prepared by the comparatively cheapsulfonated aromatic hydrocarbon electrolyte XI and the electrodecatalyst covering solution XI is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfopropylated sulfon membrane/electrode assembly unlike the cheapsulfonated aromatic hydrocarbon membrane/electrode assembly (seeComparative example 5-(3) is as stable as the expensiveperfluorosulfonic membrane/electrolyte assembly, and satisfies both lowcost and high performance.

(4) Evaluation of Output of the Unit Cells of a Fuel Cell

We evaluated the output performance of a fuel cell by dipping saidmembrane/electrode assembly X in deionized boiling water for 2 hours tolet the assembly absorb water and setting the wet membrane/electrodeassembly X in a sample unit. FIG. 12 shows a relationship betweencurrent density and voltage of a unit cell of a fuel cell containingmembrane/electrode assembly Xl. The output voltage of the fuel cell is0.68 V at a current density of 1 A/cm² and 0.81 V at a current densityor 300 mA/cm². This fuel cell is fully available as a solid polymerelectrolyte fuel cell.

We ran the unit cell of said solid polymer electrolyte fuel cell for along time at a current density of 300 mA/cm². FIG. 13 shows therelationship between the output voltage and the running time of the unitcell. The curve 30 in FIG. 13 is the result of the endurance test of theunit cell using the membrane/electrode assembly X in accordance with thepresent invention. The curve 31 in FIG. 13 is the result of theendurance test of the unit cell using a perfluorosulfonicmembrane/electrode assembly. As shown by curve 30 in FIG. 13, the outputvoltage of the unit cell is initially 0.81 V and keeps at the samevoltage level even after the unit cell runs 5,000 hours, which is thesame as the behavior of the output voltage of the unit cell using aperfluorosulfonic membrane (by curve 31). As shown by curve 32 in FIG.13, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example 5 below) is initially0.63 V but completely exhausted after the fuel cell runs 600 hours.Judging from these, it is apparent that the unit cell of a fuel cellusing an aromatic hydrocarbon electrolyte having a sulfonic group bondedto the aromatic ring via an alkyl group is more durable than the unitcell of a fuel cell using an aromatic hydrocarbon electrolyte having asulfonic group directly bonded to the aromatic ring. Further, althoughboth membrane/electrode assemblies of Embodiment 6 and Comparativeexample 5 carry 0.25 mg/cm² of platinum, the output voltage ofEmbodiment 6 is greater than the output voltage of Comparative example5. This is because the ion conductivities of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Embodiment 6 are greater than those of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Comparative example 5 and because the membrane/electrode assembly ofEmbodiment 6 is superior to the membrane/electrode assembly ofComparative example 5.

(5) Preparation of Fuel Cells

We piled up 36 unit cells which were prepared in (5) to form a solidpolymer electrolyte fuel cell as shown in FIG. 3. This fuel cell outputs3 KW.

COMPARATIVE EXAMPLE 5 (1) Preparation of Sulfonated Poly-Sulfone

We prepared sulfonated poly-sulfone by setting up a 500-ml 4-neck roundbottom flask with a reflux condenser, a stirrer, a thermometer, and adesiccant tube (containing calcium chloride in it), substituting the airinside the flask by nitrogen gas, putting 25 g of poly-sulfone (PSU) and125 ml of concentrated sulfuric acid in the flask, stirring the mixtureat a room temperature for one night in the flow of nitrogen gas to makea uniform solution, dripping 48 ml of chlorosulfuric acid first slowly(because the chlorosulfuric acid vigorously reacts with water in thesulfuric acid with bubbles) by a dropping funnel into the uniformsolution in the flow of nitrogen gas, completing dripping within 5minutes after bubbling calms down, stirring the reactant solution at 25°C. for three and half hours to sulfonate thereof, dripping the reactantsolution slowly into 15 liters of deionized water, filtering thedeionized water to recover the precipitate (sulfonatedpoly-ethersulfone), repeating mixing the precipitate with deionizedwater and suction-filtering the mixture until the filtrate becomesneutral, and vacuum-drying the precipitate at 80° C. for one night. Theion exchange group equivalent weight of the obtained sulfonatedpoly-sulfone electrolyte is 700 g/mol.

We put 1.0 g of obtained sulfonated polysulfone electrolyte and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured the ion exchange group equivalent weight of sulfonatedpolysulfone. As the result, we found that the ion exchange groupequivalent weight of sulfonated polysulfone electrolyte is 3,000 g/molwhich is greater than the initial ion exchange group equivalent weight(700 g/mol). This means that the sulfonic groups are dissociated.

(2) Preparation of an Electrolyte Membrane

We prepared an electrolyte membrane XI by dissolving sulfonatedpolysulfone electrolyte obtained by the above procedure (1) into amixture of 20 parts of N,N′-dimethylformamide, 80 parts of cyclohexanon,and 25 parts of methylethylketone so that the solution may contain 5% byweight of the product, spreading this solution over a glass plate byspin-coating, air-drying thereof, and vacuum-drying thereof at 80° C.The obtained electrolyte membrane Xl is 45 μm thick and its ion exchangegroup equivalent is 0.02 S/cm.

We put said obtained electrolyte membrane XI and 20 ml of deionizedwater in a TEFLON-coated hermetic stainless steel container and kept thecontainer at 120° C. for 2 weeks. As the result, we found theelectrolyte membrane XI broken and ragged.

(3) Preparation of a Solution for Covering Electrode Catalyst and aMembrane/Electrode Assembly

We prepared a solution XI for covering electrode catalyst by adding asolvent mixture of N,N′-dimethylformamide, cyclohexanon, andmethylethylketone which contains 5% by weight of the product (see (2))to carbon carrying 40% by weight of platinum so that the ratio by weightof platinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly XI by coating both sides of the electrolyte membrane XI(obtained by (2)) with said solution XI for covering electrode catalyst,and drying thereof. The obtained membrane/electrode assembly XI carries0.25 mg/cm² of platinum.

We put said obtained membrane/electrode assembly XI and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and theninspected thereof. As the result, we found the membrane/electrodeassembly XI broken and ragged.

(4) Endurance Test of Unit Cells of a Fuel Cell

We assembled the membrane/electrode assembly XI of Comparative example5, thin carbon-paper packing materials (as supporting currentcollectors) at both sides of the assembly, and conductive separators(bipolar plates) provided at outer sides thereof and also working toseparate the electrodes from the chamber and to flow gases to theelectrodes into a unit cell for a solid polymer electrolyte fuel cell,and ran the unit cell for a long time at a current density of 300mA/cm². As the result, the output voltage of the unit cell was initially0.68V but exhausted after a 600-hours run, as shown by the curve 32 inFIG. 13.

EMBODIMENT 7 (1) Preparation of Sulfo-Propylated Polysulfone

We prepared sulfo-propylated poly-sulfone electrolyte by setting up a500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 22.1 g ofpolysulfone (PSU), 12.2 g (0.1 mol) of propane-sultone and 50 ml of drynitrobenzene, adding 14.7 g (0.11 mol) of aluminum chloride anhydride tothe mixture gradually for 30 minutes while stirring thereof, thenrefluxing for 24 hours, dripping the reactant solution into 500 ml oficed water containing 25 ml of concentrated hydrochloric acid to stopthe reaction, separating the organic precipitate, washing thereof,neutralizing thereof with an aqueous solution of sodium carbonatecontaining a few drops of octyl alcohol, separating aluminum hydroxideby filtration, decoloring the filtrate by active carbon, and evaporatingthe solvent. The ion exchange group equivalent weight of the obtainedsulfo-propylated polysulfone electrolyte is 660 g/mol.

The cost of the sulfo-propylated sulfone electrolyte is one fiftieth orunder of the cost of perfluoro-sulfonic electrolyte which is preparedfrom expensive material in five processes because the sulfo-propylatedsulfone electrolyte is prepared in a single process from poly-sulfonewhich is very cheap engineering plastics on-market.

We put 1.0 g of obtained sulfo-propylated polysulfone and 20 ml ofdeionized water in a TEFLON-coated hermetic stainless steel container,kept the container at 120° C. for 2 weeks, cooled the container and thenmeasured the ion exchange group equivalent weight of the resiltingsulfo-propylated polysulfone electrolyte. As the result, we found thatthe ion exchange group equivalent weight of sulfo-propylated sulfoneremains unchanged (660 g/mol) and that sulfo-propylated sulfone is asstable as the expensive perfluoro-sulfonic electrolyte. Contrarily asshown by the comparative example 5-(1) below, the cheap sulfonatedaromatic hydrocarbon electrolyte is deteriorated under the sametemperature and hydrolysis condition. Its ion exchange group equivalentincreases up to 3,000 g/mol (which was initially 700 g/mol) and sulfonegroups were dissociated. In other words, the low-cost sulfo-propylatedsulfone electrolyte unlike the cheap sulfonated aromatic hydrocarbonelectrolyte (see Comparative example 5-(1)) shows very good chemicalstability as well as the expensive perfluoro-sulfonic electrolyte,satisfying both low cost and high performance.

(2) Preparation of an Electrolyte Membrane

We prepared an electrolyte membrane by dissolving the product obtainedby the above procedure (1) into a mixture of trichloroethane anddichloroethane (1:1) so that the solution may contain 5% by weight ofthe product, spreading this solution over a glass plate by spin-coating,air-drying thereof, and vacuum-drying thereof at 80° C. The obtainedsulfo-propylated poly-sulfone electrolyte membrane X is 38 μm thick.

We put said obtained sulfo-propylated poly-sulfone electrolyte membraneX and 20 ml of deionized water in a TEFLON-coated hermetic stainlesssteel container, kept the container at 120° C. for 2 weeks, cooled thecontainer and then measured its ion exchange group equivalent weight. Asthe result, we found that the ion exchange group equivalent weight ofthe obtained electrolyte membrane remains unchanged as well as theexpensive perfluoro-sulfonic electrolyte. The membrane itself is toughenough. Contrarily as shown by the comparative example 5-(2), thecomparatively cheap sulfonated aromatic hydrocarbon electrolyte XI isbroken and ragged under the same temperature and hydrolysis condition.In other words, the low-cost sulfo-propylated poly-sulfone electrolyteunlike the cheap sulfonated aromatic hydrocarbon electrolyte (seeComparative example 5-(2)) shows very good chemical stability as well asthe expensive perfluoro-sulfonic electrolyte, satisfying both low costand high performance.

(3) Preparation of a Solution for Covering Electrode Catalyst and aMembrane/Electrode Assembly

We prepared a solution for covering electrode catalyst by adding asolvent mixture of trichloro-ethane and dichloro-ethane (see (2)) tocarbon carrying 40% by weight of platinum so that the ratio by weight ofplatinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly by coating both sides of the electrolyte membrane (obtained by(2)) with said solution for covering electrode catalyst, and dryingthereof. The obtained membrane/electrode assembly carries 0.25 mg/cm² ofplatinum.

We put said obtained membrane/electrode assembly and 20 ml of deionizedwater in a TEFLON-coated hermetic stainless steel container and kept thecontainer at 120° C. for 2 weeks. As the result, we found that the ionexchange group equivalent weight of the obtained electrolyte membraneremains unchanged as well as the membrane/electrode assembly preparedfrom the expensive perfluoro-sulfonic membrane and theperfluoro-sulfonic electrolyte. The membrane itself is tough enough.

Contrarily as shown by the comparative example 5-(3), themembrane/electrode assembly prepared by the comparatively cheapsulfonated aromatic hydrocarbon electrolyte and the electrode catalystcovering solution is broken and ragged under the same temperature andhydrolysis condition. In other words, the low-cost sulfo-propylatedsulfon membrane/electrode assembly unlike the cheap sulfonated aromatichydrocarbon membrane/electrode assembly (see Comparative example 5-(3))is as stable as the expensive perfluoro-sulfonic membrane/electrolyteassembly, and satisfies both low cost and high performance.

(4) Evaluation of Output of the Unit Cells of a Fuel Cell

We evaluated the output performance of a fuel cell by dipping saidmembrane/electrode assembly in deionized boiling water for 2 hours tolet the assembly absorb water and setting the wet membrane/electrodeassembly in a sample unit. FIG. 14 shows a relationship between currentdensity and voltage of a unit cell of a fuel cell containingmembrane/electrode assembly. The output voltage of the fuel cell is 0.75V at a current density of 1 A/cm² and 0.83 V at a current density or 300mA/cm². This fuel cell is fully available as a solid polymer electrolytefuel cell.

We ran the unit cell of said solid polymer electrolyte fuel cell for along time at a current density of 300 mA/cm². FIG. 15 shows therelationship between the output voltage and the running time of the unitcell. The curve 33 in FIG. 15 is the result of the endurance test of theunit cell using the membrane/electrode assembly in accordance with thepresent invention. The curve 34 in FIG. 15 is the result of theendurance test of the unit cell using a perfluoro-sulfonicmembrane/electrode assembly. As shown by curve 33 in FIG. 15, the outputvoltage of the unit cell is initially 0.83 V and keeps at the samevoltage level even after the unit cell runs 5,000 hours, which is thesame as the behavior of the output voltage of the unit cell using aperfluoro-sulfonic membrane (by curve 34). As shown by curve 35 in FIG.15, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example 5 below) is initially0.63 V but completely exhausted after the fuel cell runs 600 hours.Judging from these, it is apparent that the unit cell of a fuel cellusing an aromatic hydrocarbon electrolyte having a sulfonic group bondedto the aromatic ring via an alkyl group is more durable than the unitcell of a fuel cell using an aromatic hydrocarbon electrolyte having asulfonic group directly bonded to the aromatic ring. Further, althoughboth membrane/electrode assemblies of Embodiment 7 and Comparativeexample 5 carry 0.25 mg/cm² of platinum, the output voltage ofEmbodiment 7 is greater than the output voltage of Comparative example5. This is because the ion conductivities of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Embodiment 7 are greater than those of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Comparative example 5 and because the membrane/electrode assembly ofEmbodiment 7 is superior to the membrane/electrode assembly ofComparative example 5.

(6) Preparation of Fuel Cells

We piled up 36 unit cells which were prepared in (5) to form a solidpolymer electrolyte fuel cell as shown in FIG. 3. This fuel cell outputs3 KW.

EMBODIMENT 8 TO EMBODIMENT 13

We prepared sulfo-alkylated aromatic hydrocarbon electrolyte by settingup a 500-ml 4-neck round bottom flask with a reflux condenser, astirrer, a thermometer, and a desiccant tube (containing calciumchloride in it), substituting the air inside the flask by nitrogen gas,putting an aromatic hydrocarbon polymer, a sultone, and 50 ml of drynitrobenzene in the flask, adding 14.7 g (0.11 mol) of aluminum chlorideanhydride to the mixture gradually for 30 minutes while stirringthereof, refluxing the mixture at a preset temperature for a preset timeperiod after addition of aluminum chloride anhydride is completed,pouring the reactant into 150 ml of iced water containing 25 ml ofconcentrated hydrochloric acid to stop the reaction, dripping thereactant solution slowly into 0.5 liter of deionized water, filteringthe deionized water to recover the precipitate (sulfo-alkylated aromatichydrocarbon), repeating mixing the precipitate with deionized water andsuction-filtering the mixture until the filtrate becomes neutral, andvacuum-drying the precipitate at 120° C. for one night. We measured andevaluated the water resistance, and deterioration of the electrolyte andthe membrane/electrode assembly, and performance of the unit cell of afuel cell made thereof. Table 1 shows the result of evaluation andmeasurement. The cost of the sulfo-alkylated aromatic hydrocarbonelectrolyte is one fortieth or under of the cost of perfluoro-sulfonicelectrolyte which is prepared from expensive material in five processesbecause the sulfo-alkylated aromatic hydrocarbon electrolyte is preparedin a single process from very cheap engineering plastics on-market. Weput respective sulfo-alkylated aromatic hydrocarbon electrolytes ofEmbodiment 8 to Embodiment 13 and deionized water in a TEFLON-coatedhermetic stainless steel container, kept each container at 120° C. for 2weeks, and measured the ion exchange group equivalent weight of eachsulfo-alkylated aromatic hydrocarbon electrolytes. As the result, wefound that each of sulfo-alkylated aromatic hydrocarbon electrolytesunlike the cheap sulfonated aromatic hydrocarbon of Comparative example1 keeps its initial value and is as stable as the expensiveperfluoro-sulfonic electrolyte, satisfying the low cost and highperformance. We put respective sulfo-alkylated aromatic hydrocarbonelectrolytes of Embodiment 8 to Embodiment 13 and deionized water in aTEFLON-coated hermetic stainless steel container, kept each container at120° C. for 2 weeks, and measured the ion exchange group equivalentweight of each sulfo-alkylated aromatic hydrocarbon electrolytes. As theresult, we found that each of sulfo-alkylated aromatic hydrocarbonelectrolytes unlike the cheap sulfonated aromatic hydrocarbon ofComparative example 1 keeps its original shape and is as stable as theexpensive perfluoro-sulfonic electrolyte, satisfying the low cost andhigh performance. We put respective sulfo-alkylated aromatic hydrocarbonmembrane/electrode assemblies of Embodiment 8 to Embodiment 13 anddeionized water in a TEFLON-coated hermetic stainless steel containerand kept each container at 120° C. for 2 weeks. We found that each ofthe sulfo-alkylated aromatic hydrocarbon membrane/electrode assembliesunlike the sulfonated aromatic hydrocarbon of Comparative example 1keeps its original property and is as stable as the expensiveperfluoro-sulfonic membrane/electrode assembly, satisfying the low costand high performance. Further after running respective unit cells at 300mA/cm² for 5,000 hours, we found that the output of respective unitcells using sulfo-alkylated aromatic hydrocarbon electrolytes unlike theoutput of a unit cell using the sulfonated aromatic hydrocarbonelectrolyte of Comparative example 1 keeps the initial output voltageand is as stable as the unit cell using the expensive perfluoro-sulfonicelectrolyte, satisfying the low cost and high performance. TABLE 1Embodiment Embodiment Embodiment Embodiment Embodiment Embodiment 8 9 1011 12 13 Aromatic hydrocarbon Poly-allyl- Poly-ketone Poly-ether-Poly-ether- Poly-ether- Poly-ether- polymer (g) ether- (12.0) ketonesulfone sulfone sulfone ketone (15.0) (20.0) (5.0) (11.6) (14.0) Sultone(g) Propane- Propane- Propane- Propane- Propane- Butane- sultone sultonesultone sultone sultone sultone (12.2) (12.2) (12.2) (12.2) (25.5)(13.6) Temperature of reaction 150 150 150 150 150 150 (° C.) Time ofreaction (hr) 12 12 12 5 30 30 Ion exchange group 620 610 680 1000 250680 equivalent weight (g/mol) Ion exchange group 620 610 680 1000 250680 equivalent weight of electrolyte after dipping in deionized water at120° C. for 2 weeks (g/mol) Ion exchange group No change No change Nochange No change No change No change equivalent weight of membrane afterdipping in deionized water at 120° C. for 2 weeks Ion exchange group Nochange No change No change No change No change No change equivalentweight of membrane/electrode assembly after dipping in deionized waterat 120° C. for 2 weeks Initial output of unit 0.65 0.66 0.65 0.6 0.690.65 cell (V at 1 A/cm²) Output of unit cell 97 98 96 97 96 95 afterrunning at 300 mA/cm² for 5,000 hours (ratio to the initial voltage inpercentage)

EMBODIMENT 14 (1) Preparation of Chloromethylated Poly-Ether Sulfone

We prepared chloromethylated poly-ether sulfone by setting up a 500-ml4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 21.6 g ofpoly-ether sulfone (PES), 60 g (2 moles) of paraformaldehyde and 50 mlof dry nitro benzene, blowing 73 g of hydrogen chloride gas whilestirring at 100° C., keeping the mixture at 150° C., dripping thereactant solution slowly into 1 liter of deionized water, lettingchloromethylated poly-ether sulfone deposit, filtrating and recoveringthe precipitate repeating mixing the precipitate with deionized waterand suction-filtering the mixture until the filtrate becomes neutral,and vacuum-drying the precipitate at 80° C. for one night.

(2) Preparation of Sulfo-Methylated Poly-Ether Sulfone.

We prepared sulfo-methylated poly-ether sulfone by setting up a 500-ml4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 10 g ofchloro-methylated poly-ether sulfone, 50 ml of dry nitro benzene, and 30g of sodium sulfate, stirring the mixture at 100° C. for 5 hours, adding10 ml of deionized water, stirring the solution for five hours, drippinga reactant solution slowly into 1 liter of deionized water, lettingsulfo-methylated poly-ether sulfone deposit, filtrating and recoveringthe precipitate repeating mixing the precipitate with deionized waterand suction-filtering the mixture until the filtrate becomes neutral,and vacuum-drying the precipitate at 120° C. for one night. The ionexchange group equivalent weight of the resulting sulfo-methylatedpoly-ether sulfone electrolyte is 600 g/mol.

As the sulfo-methylated poly-ether sulfone electrolyte in accordancewith the present invention can be produced in two processes frompoly-poly-ether-sulfone which is inexpensive engineering plasticson-market, the cost of the sulfo-methylated poly-ether sulfoneelectrolyte is one thirtieth or under of the perfluorosulfonicelectrolyte which is produced in five processes from expensivematerials. However, the method of producing the sulfoalkylatedpoly-ether sulfone electrolyte by sulfoalkylatingpoly-poly-ether-sulfone directly by sultone (as in Embodiment 1) has oneprocess less than the method of Embodiment 14. Therefore the cost of thesulfoalkylated poly-ether sulfone electrolyte is two third of the costof product obtained by the method of Embodiment 14. Namely, the methodof sulfoalkylating sulfoalkylating poly-poly-ether-sulfone directly bysultone is lower-costed.

We put 1.0 g of the obtained sulfo-methylated poly-ether sulfoneelectrolyte and 20 ml of deionized water in a TEFLON-coated hermeticstainless steel container, kept the container at 120° C. for 2 weeks,cooled the container and then measured the ion exchange group equivalentweight of sulfo-methylated poly-ether sulfone electrolyte. As theresult, we found that the ion exchange group equivalent weight of thesulfopropylated polyether sulfone electrolyte remains unchanged (600g/mol) and that sulfopropylated polyether sulfone is as stable as theexpensive perfluorosulfonic electrolyte. Contrarily as shown by theComparative example 1-(1) below, the cheap sulfonated aromatichydrocarbon electrolyte is deteriorated under the same temperature andhydrolysis condition. Its ion exchange group equivalent increases up to3,000 g/mol (which was initially 960 g/mol) and sulfone groups weredissociated. In other words, the low-cost sulfo-methylated poly-ethersulfone electrolyte unlike the cheap sulfonated aromatic hydrocarbonelectrolyte shows very good chemical stability as well as the expensiveperfluorosulfonic electrolyte, satisfying both low cost and highperformance.

(3) Preparation of an Electrolyte Membrane

We prepared an electrolyte membrane by dissolving the sulfo-methylatedpoly-ether-sulfone electrolyte obtained by the above procedure (2) intoa mixture of trichloroethane and dichloroethane (1:1) so that thesolution may contain 5% by weight of the product, spreading thissolution over a glass plate by spin-coating, air-drying thereof, andvacuum-drying thereof at 80° C. The obtained sulfo-methylatedpoly-ether-sulfone electrolyte membrane is 42 μm thick.

We put said obtained sulfo-methylated poly-ether-sulfone electrolytemembrane and 20 ml of deionized water in a TEFLON-coated hermeticstainless steel container and kept the container at 120° C. for 2 weeks.As the result, we found that the ion exchange group equivalent weight ofthe obtained electrolyte membrane remains unchanged as well as theexpensive perfluoro-sulfonic electrolyte. The membrane itself is toughenough. Contrarily as shown by the comparative example 1-(2), thecomparatively cheap sulfonated aromatic hydrocarbon electrolyte isbroken and ragged under the same temperature and hydrolysis condition.In other words, the low-cost sulfo-methylated poly-ether-sulfoneelectrolyte unlike the cheap sulfonated aromatic hydrocarbon electrolyteshows very good chemical stability as well as the expensiveperfluoro-sulfonic electrolyte, satisfying both low cost and highperformance.

(4) Preparation of a Solution for Covering Electrode Catalyst and aMembrane/Electrode Assembly

We prepared a paste (solution for covering electrode catalyst) by addinga solvent mixture of trichloro-ethane and di-chloro-ethane (see (3)) tocarbon carrying 40% by weight of platinum so that the ratio by weight ofplatinum catalyst and the polymer electrolyte might be 2:1, anddispersing the mixture uniformly. Next we prepared a membrane/electrodeassembly by coating both sides of the electrolyte membrane (obtained by(2)) with said solution for covering electrode catalyst, and dryingthereof. The obtained membrane/electrode assembly carries 0.25 mg/cm² ofplatinum.

We put the obtained membrane/electrode assembly and 20 ml of deionizedwater in a TEFLON-coated hermetic stainless steel container and kept thecontainer at 120° C. for 2 weeks. As the result, we found that theproperty of the membrane/electrode assembly keeps its initial propertyas well as the expensive perfluoro-sulfonic membrane/electrode assemblyprepared by the expensive perfluoro-sulfonic membrane and theperfluoro-sulfonic electrolyte. Its membrane is tough enough. Contrarilyas shown by the comparative example 1-(3), the membrane/electrodeassembly prepared by the comparatively cheap sulfonated aromatichydrocarbon electrolyte membrane 11 and the electrode catalyst coveringsolution II is deteriorated under the same temperature and hydrolysiscondition. The electrodes are separated from the assembly. In otherwords, the low-cost sulfomethylated polyether sulfone membrane/electrodeassembly unlike the cheap sulfonated aromatic hydrocarbonmembrane/electrode assembly (see Comparative example 1-(3)) shows verygood chemical stability as well as the expensive perfluoro-sulfonicelectrolyte, satisfying both low cost and high performance.

(5) Evaluation of Output of the Unit Cells of a Fuel Cell

We evaluated the output performance of a fuel cell by dipping saidmembrane/electrode assembly in deionized boiling water for 2 hours tolet the assembly absorb water and setting the wet membrane/electrodeassembly in a sample unit. FIG. 16 shows a relationship between currentdensity and voltage of a unit cell of a fuel cell containingmembrane/electrode assembly. The output voltage of the fuel cell is 0.68V at a current density of 1 A/cm² and 0.82 V at a current density or 300mA/cm². This fuel cell is fully available as a solid polymer electrolytefuel cell.

We ran the unit cell of said solid polymer electrolyte fuel cell for along time at a current density of 300 mA/cm². FIG. 17 shows therelationship between the output voltage and the running time of the unitcell. The curve 36 in FIG. 17 is the result of the endurance test of theunit cell using the membrane/electrode assembly in accordance with thepresent invention. The curve 37 in FIG. 17 is the result of theendurance test of the unit cell using a perfluoro-sulfonicmembrane/electrode assembly. As shown by curve 36 in FIG. 17, the outputvoltage of the unit cell is initially 0.82 V and keeps at the samevoltage level even after the unit cell runs 5,000 hours, which is thesame as the behavior of the output voltage of the unit cell using aperfluoro-sulfonic membrane (by curve 37). As shown by curve 38 in FIG.17, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example) is initially 0.73 V butcompletely exhausted after the fuel cell runs 600 hours. Judging fromthese, it is apparent that the unit cell of a fuel cell using anaromatic hydrocarbon electrolyte having a sulfonic group bonded to thearomatic ring via an alkyl group is more durable than the unit cell of afuel cell using an aromatic hydrocarbon electrolyte having a sulfonicgroup directly bonded to the aromatic ring. Further, although bothmembrane/electrode assemblies of Embodiment 14 and Comparative example 1carry 0.25 mg/cm² of platinum, the output voltage of Embodiment 14 isgreater than the output voltage of Comparative example 4. This isbecause the ion conductivities of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofEmbodiment 14 are greater than those of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Comparative example 1 and because the membrane/electrode assembly ofEmbodiment 14 is superior to the membrane/electrode assembly ofComparative example 1.

(6) Preparation of Fuel Cells

We piled up 36 unit cells which were prepared in (5) to form a solidpolymer electrolyte fuel cell as that shown in FIG. 3. This fuel celloutputs 3 KW.

EMBODIMENT 15 (1) Preparation of Bromo-Hexamethylated Poly-Ether Sulfone

We prepared bromo-hexamethylated poly-ether sulfone by setting up a500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 23.2 g ofpolyether sulfone (PES) and 50 ml of dry nitrobenzene in the flask,adding 6.5 g of butoxylithium to the mixture, keeping the mixture at theroom temperature for 2 hours, adding 100 g of 1,6-dibromohexane to themixture, stirring thereof for 12 hours, dripping the reactant solutionslowly into 1 liter of deionized water, filtering the deionized water torecover the precipitate (bromo-hexamethylated poly-ether sulfone),repeating mixing the precipitate with deionized water andsuction-filtering the mixture until the filtrate becomes neutral, andvacuum-drying the precipitate at 120° C. for one night.

(2) Preparation of Sulfo-Hexamethylated Poly-Ether Sulfone

We prepared sulfo-hexamethylated poly-ether sulfone by setting up a500-ml 4-neck round bottom flask with a reflux condenser, a stirrer, athermometer, and a desiccant tube (containing calcium chloride in it),substituting the air inside the flask by nitrogen gas, putting 10 g ofbromo-hexamethylated poly-ether sulfone, 50 ml of dry nitrobenzene, and30 g of sodium sulfate in the flask, stirring the mixture at 100° C. for5 hours, adding 10 ml of deionized water to the mixture, stirring themixture for 5 hours, dripping the reactant solution slowly into 1 literof deionized water, filtering the deionized water to recover theprecipitate (sulfo-hexamethylated poly-ether sulfone), repeating mixingthe precipitate with deionized water and suction-filtering the mixtureuntil the filtrate becomes neutral, and vacuum-drying the precipitate at120° C. for one night. The ion exchange group equivalent weight of theobtained sulfo-hexamethylated poly-ether sulfone is 600 g/mol.

The cost of the sulfoalkylated poly-ether sulfone electrolyte in thepresent method is one thirtieth or under of the cost ofperfluoro-sulfonic electrolyte which is prepared from expensivematerials in five processes because the sulfoalkylated poly-ethersulfone electrolyte is prepared in a two processes frompoly-poly-ether-sulfone which is very cheap engineering plasticson-market. However, the method of producing the sulfoalkylatedpoly-ether sulfone electrolyte by sulfoalkylatingpoly-poly-ether-sulfone directly by sultone (as in Embodiment 1) has oneprocess less than the method of Embodiment 14. Therefore the cost of thesulfoalkylated poly-ether sulfone electrolyte is two third of the costof product obtained by the method of Embodiment 14. Namely, the methodof sulfoalkylating poly-poly-ether-sulfone directly by sultone has alower cost.

We put 1.0 g of the obtained sulfo-hexamethylated poly-ether sulfoneelectrolyte and 20 ml of deionized water in a TEFLON-coated hermeticstainless steel container, kept the container at 120° C. for 2 weeks,cooled the container and then measured the ion exchange group equivalentweight of sulfo-hexamethylated poly-ether sulfone electrolyte. As theresult, we found that the ion exchange group equivalent weight of thesulfo-hexamethylated polyether sulfone electrolyte remains unchanged(600 g/mol) and that sulfopropylated polyether sulfone is as stable asthe expensive perfluorosulfonic electrolyte. Contrarily as shown by theComparative example 1-(1) below, the cheap sulfonated aromatichydrocarbon electrolyte is deteriorated under the same temperature andhydrolysis condition. Its ion exchange group equivalent increases up to3,000 g/mol (which was initially 960 g/mol) and sulfone groups weredissociated. In other words, the low-cost sulfo-hexamethylatedpoly-ether sulfone electrolyte unlike the cheap sulfonated aromatichydrocarbon electrolyte shows very good chemical stability as well asthe expensive perfluorosulfonic electrolyte, satisfying both low costand high performance.

(3) Preparation of an Electrolyte Membrane

We prepared an electrolyte membrane by dissolving the product obtainedin the above procedure (2) into a mixture of 20 parts ofN,N′-dimethylformamide, 80 parts of cyclohexanon, and 25 parts ofmethylethylketone so that the solution may contain 5% by weight of theproduct, spreading this solution over a glass plate by spin-coating,air-drying thereof, and vacuum-drying thereof at 80° C. The obtainedsulfo-hexamethylated poly-ether sulfone electrolyte membrane is 42 μmthick and its ion exchange group equivalent is 8 S/cm.

We put the obtained sulfo-hexamethylated poly-ether sulfone electrolytemembrane and 20 ml of deionized water in a TEFLON-coated hermeticstainless steel container and kept the container at 120° C. for 2 weeks.As the result, we found that the ion exchange group equivalent weight ofthe product remains unchanged and is as stable as the expensiveperfluoro-sulfonic electrolyte. Its membrane is tough enough. Contrarilyas shown by the comparative example 1-(2) below, the cheap sulfonatedaromatic hydrocarbon electrolyte is broken and ragged under the sametemperature and hydrolysis condition. In other words, the low-costsulfo-hexamethylated poly-ether sulfone electrolyte membrane unlike thecheap sulfonated aromatic hydrocarbon electrolyte shows very goodchemical stability as well as the expensive perfluoro-sulfonicelectrolyte, satisfying both low cost and high performance.

(4) Preparation of an Electrolyte Membrane

We prepared a paste (an electrolyte catalyst covering solution) bydissolving the product (3) into a mixture of trichloroethane anddichloroethane, adding this mixture to carbon carrying 40% by weight ofplatinum so that the weight ration of platinum catalyst and polymerelectrolyte may be 2:1, and dispersing thereof uniformly. Next weprepared a membrane/electrode assembly by coating both sides of theelectrolyte membrane (obtained by (3)) with said electrode coveringsolution, and drying thereof. The obtained membrane/electrode assemblycarries 0.25 mg/cm² of platinum.

We put the obtained sulfo-hexamethylated poly-ether sulfone electrolytemembrane and 20 ml of deionized water in a TEFLON-coated hermeticstainless steel container and kept the container at 120° C. for 2 weeks.As the result, we found that the resulting membrane/electrode assemblyremains unchanged and is as stable as the membrane/electrode assemblymade from the expensive perfluoro-sulfonic membrane and theperfluoro-sulfonic electrolyte. Its membrane is tough enough. Contrarilyas shown by the comparative example 1-(3) below, the cheap sulfonatedaromatic hydrocarbon electrolyte II prepared by the comparatively cheapsulfonated aromatic hydrocarbon electrolyte membrane II and theelectrolyte catalyst covering solution II is broken and ragged under thesame temperature and hydrolysis conditions and the electrodes areseparated from the assembly. In other words, the low-costsulfo-hexametylated polyether sulfone membrane/electrode assembly unlikethe cheap sulfonated aromatic hydrocarbon electrolyte (see Comparativeexample 1-(3)) shows very good chemical stability as well as theexpensive perfluoro-sulfonic membrane/electrode assembly, satisfyingboth low cost and high performance.

(5) Evaluation of Output of the Unit Cells of a Fuel Cell

We evaluated the output performance of a fuel cell by dipping saidmembrane/electrode assembly in deionized boiling water for 2 hours tolet the assembly absorb water and setting the wet membrane/electrodeassembly in a sample unit. FIG. 18 shows a relationship between currentdensity and voltage of a unit cell of a fuel cell containingmembrane/electrode assembly. The output voltage of the fuel cell is 0.68V at a current density of 1 A/cm² and 0.83 V at a current density or 300mA/cm². This fuel cell is fully available as a solid polymer electrolytefuel cell.

We ran the unit cell of said solid polymer electrolyte fuel cell for along time at a current density of 300 mA/cm². FIG. 19 shows therelationship between the output voltage and the running time of the unitcell. The curve 39 in FIG. 19 is the result of the endurance test of theunit cell using the membrane/electrode assembly in accordance with thepresent invention. The curve 40 in FIG. 19 is the result of theendurance test of the unit cell using a perfluoro-sulfonicmembrane/electrode assembly. As shown by curve 39 in FIG. 19, the outputvoltage of the unit cell is initially 0.83 V and keeps at the samevoltage level even after the unit cell runs 5,000 hours, which is thesame as the behavior of the output voltage of the unit cell using aperfluoro-sulfonic membrane (by curve 40). As shown by curve 41 in FIG.19, the output voltage (of a unit cell using sulfonated aromatichydrocarbon electrolyte of Comparative example 1) is initially 0.73 Vbut completely exhausted after the fuel cell runs 600 hours. Judgingfrom these, it is apparent that the unit cell of a fuel cell using anaromatic hydrocarbon electrolyte having a sulfonic group bonded to thearomatic ring via an alkyl group is more durable than the unit cell of afuel cell using an aromatic hydrocarbon electrolyte having a sulfonicgroup directly bonded to the aromatic ring. Further, although bothmembrane/electrode assemblies of Embodiment 15 and Comparative example 1carry 0.25 mg/cm² of platinum, the output voltage of Embodiment 15 isgreater than the output voltage of Comparative example 4. This isbecause the ion conductivities of the electrolyte and the electrodecatalyst covering solution in the membrane/electrode assembly ofEmbodiment 15 are greater than those of the electrolyte and theelectrode catalyst covering solution in the membrane/electrode assemblyof Comparative example 1 and because the membrane/electrode assembly ofEmbodiment 15 is superior to the membrane/electrode assembly ofComparative example 1.

(6) Preparation of Fuel Cells

We piled up 36 unit cells which were prepared in (5) to form a solidpolymer electrolyte fuel cell as that shown in FIG. 3. This fuel celloutputs 3 KW.

EFFECT OF THE INVENTION

The sulfoalkylated aromatic hydrocarbon electrolyte in accordance withthe present invention can be produced in a single process from low-costengineering plastics and its cost is one fortieth or under of a fluorineelectrolyte membrane represented by a perfluoro-sulfonic membrane whichis produced in five processes from expensive materials. Further due tothe bonding of a sulfonic group to a benzene ring via an alkyl groupunlike the direct bonding of a sulfonic group to a benzene ring, the ionconductivity of the sulfoalkylated aromatic hydrocarbon electrolyte isgreat, suppresses sulfonic groups from being dissociated at a hightemperature in the presence of a strong acid, and shows a substantiallyhigh chemical durability. Therefore, electrolyte membranes, electrolytecatalyst covering solutions, membrane/electrode assemblies, and fuelcells using the sulfoalkylated aromatic hydrocarbon electrolyte inaccordance with the present invention show a substantially high chemicaldurability and can reduce steps of production.

1. A fuel cell comprising: a solid polymer electrolyte membrane; and anelectrode unit comprising a cathode and an anode, which are placed oneon each side of said polymer electrolyte membrane, wherein said solidpolymer electrolyte membrane contains a solid polymer electrolyte, whichcomprises a polymer compound having a hydrocarbon aromatic group in thebackbone thereof and including a side chain expressed by FORMULA 1:

wherein “n” is 1, 2, 3, 4, 5, or
 6. 2. The fuel cell of claim 1, whereinsaid polymer compound is a poly-ether sulfonic polymer.
 3. The fuel cellof claim 1, wherein said polymer compound is a poly-ether ether ketonepolymer.
 4. The fuel cell of claim 1, wherein said polymer compound is apoly-phenylene sulfide polymer.
 5. The fuel cell of claim 1, whereinsaid polymer compound is a poly-phenylene ether polymer.
 6. The fuelcell of claim 1, wherein said polymer compound is a polysulfonicpolymer.
 7. The solid polymer electrolyte fuel cell of claim 1, whereinsaid polymer compound is a poly-ether ketone polymer.